Philly’s a tough town.If there’s a quintessential story about the City of Brotherly Love, it’s this one: In 2015, when Canadian researchers developed a child-sized hitchhiking robot with a big smile and yellow wellies, the hitchbot made it across Europe and halfway down the East Coast, offering friendly small talk to anyone it encountered. Then it got to Philadelphia, where it was promptly torn limb from limb and left in an alley.Residents have pelted Santa with snowballs and hurled batteries and beer at their own quarterback. They flip cars and set things on fire even when they win the Super Bowl and World Series.The unloved cousin of Boston and New York is often overlooked by Hollywood. The accent is so tricky to replicate, most actors won’t go near it. (Even Rocky didn’t even have a proper Philly twang.)So it’s funny, then, that it took a Brit with an elegant voice, creamy complexion and sunny outlook to parachute into the Philly burbs and totally nail the look, feel, sound and salty attitude of the denizens of Delaware County, or Delco, as it’s known.Fierce in flannel: Ms. Winslet doing some interrogating on “Mare of Easttown.” Michele K. Short/HBOKate Winslet gets emotional talking about the end of her HBO limited series, “Mare of Easttown,” which scored its own “Saturday Night Live” skit and found a fan in the self-described Philly girl in the White House, Jill Biden. (“You don’t screw around with a Philly girl,” Joe Biden said of his wife last year, after she blocked an anti-dairy activist who bum-rushed him at a campaign stop.)Ms. Winslet has said, in the past, that it’s hard for an actor to tell what will wow audiences while you’re shooting, that sometimes you think you’re doing great work and then it turns out to be “a limp biscuit.”Mare Sheehan is anything but a limp biscuit. The police detective exists in a cloud of vape smoke, trysts, flannel, Rolling Rock and Jameson shots — “a very hot grandma,” as Guy Pearce’s character calls her, sparring with a mother (Jean Smart) who loves drinking Manhattans.Ms. Winslet said that she has been bowled over by how audiences have fallen “in love with this wildly flawed, messy, broken, fragmented, difficult woman. I loved her marks and her scars and her faults and her flaws and the fact that she has no off switch, no stop button. She just knows ‘Go.’”“Not only did I have to hide myself in the character completely, but I had to hide this story, carry the secret,” she said. “I kept it hidden since 2018 when I first read the scripts. My job was to take them on this horrendous journey and hope to God that they’d be prepared to come into the attic with me at the end. It has been agony, agony, agony. You can see I’m still like … ” She sounds as if she might cry — something she would never let Mare do — then pulls herself together and lets fly one of her frequent, merry F-bombs. “I can’t deal with it. It’s ridiculous.”When your dog matches your hair (note also what appears to be a beer-tab necklace).Jamie Hawkesworth for The New York Times‘Bad Jeans’ and CheesesteakThe show is a murder mystery with many motifs: grief, the opioid crisis, small-town life. Ms. Winslet, a mother of three, sees it from this perspective: “It’s about mothers protecting their children at all costs, and the lengths that a parent will go to in order to protect their children,” she said. About the finale’s twist ending, she adds, “Oh God, it’s just unbelievable, it’s heartbreaking.”Underneath Mare’s facade, she said, “is a woman who is so entrenched in grief for her son that she has not processed, and as she shares it, as she talks about it with a therapist, she will crack. She doesn’t want affection. She doesn’t want to be loved. And she doesn’t want to be cared for because if she has to experience those things, it makes her feel vulnerable, and if she feels vulnerable, then she can’t be strong anymore, and she can’t carry on.”Ms. Winslet is known for what one producer called her “insane work ethic.” She prepares elaborate back stories for her characters, and she said she prepped more for Mare than any other role in her life. (But she is not Daniel Day-Winslet; she is said to be fun once the shooting wraps for the day.)She was Zooming in from her house on the south coast of England, curled up with bare feet, her blond mane looking much glossier than Mare’s. She’s wearing an old white Calypso T-shirt, a couple of gold necklaces and some black Sweaty Betty pants.The actress often saves something from her sets, and she shifted her camera to show off the sign from the Easttown police station she has hung on a wall. She kept Mare’s jacket and badge, too.She has been harking back to her breakout role as another strong, but more upper crust, Philly girl: Rose DeWitt Bukater. “It’s like ‘Titanic’ again,” she said, chuckling. “I’m on the side of buses again! It’s like going back in time 24 years where I’m walking down the street and people are nudging and pointing and whispering again.” When the actress was on a bike ride in England recently, a woman ran up to stroke her arm and offer all her theories about whodunit.Her heart went on: the famous shot with Mr. DiCaprio in “Titanic.”CBS, via Getty ImagesMs. Winslet said she knows people are saying, “Oh my God, how can she let herself look so unglamorous?” When Craig Zobel, the director, assured her he would cut “a bulgy bit of belly” in her sex scene with Guy Pearce, she told him, “Don’t you dare!” She also sent the show’s promo poster back twice because it was too retouched. “They were like ‘Kate, really, you can’t,’ and I’m like ‘Guys, I know how many lines I have by the side of my eye, please put them all back.’”She said she balked when she saw an early cut in which her ordinarily luminous skin looked too good. “We tried to light it to make it look not nice,” she said.She continued: “Listen, I hope that in playing Mare as a middle-aged woman — I will be 46 in October — I guess that’s why people have connected with this character in the way that they have done because there are clearly no filters. She’s a fully functioning, flawed woman with a body and a face that moves in a way that is synonymous with her age and her life and where she comes from. I think we’re starved of that a bit.“In episode one, she’s having sex on a couch. I said to my husband, ‘Am I OK with that? Is it all right that I’m playing a middle-aged woman who is a grandmother who does really make a habit of having one-night stands?’ He’s like, ‘Kate, it’s great. Let her do it.’”In moments of doubt, she tortured herself and her assistant director, wondering about other actresses — “three real people were haunting my mind, I will not name them” — who might have done a better job.The show’s costume designer did recon in Wawa, finding inspiration for Mare’s flannel, inexpensive T-shirts, Ocean City sweatshirts and “bad jeans,” as Ms. Winslet said.“Whenever we’d find something unflattering,” Ms. Winslet recalled, “we’d be jumping up and down like, ‘Yes! We’re wearing this.’”She would leave her clothes in a crumpled pile on the floor of her trailer after filming “and they would stay in a rumpled up ball overnight. We were not washing and drying and hanging those clothes. Never.”They filled in her shapely eyebrows to give her face a heavier look, and left the sunspots and imperfections. “We’re so used to seeing this stuff airbrushed away,” she said.She wanted Mare to reflect the burdens she carried, a physical and emotional “heftiness.” She borrowed a Peloton to work out at night to make her thighs more muscular. “There’s a sloppiness to her, and there’s a looseness to how she sits and how she walks and just how she holds herself,” she said. “Her body posture is totally different to mine. I actually stand quite upright.”In one peak-Mare scene, she comes home and scarfs down a cheesesteak that her mother has gotten her, without taking off her jacket, still clutching her police files. “This is so clearly a woman who does not cook, doesn’t care about what she puts into her mouth, also probably forgets to eat, so that when she does eat, she’s so starving, she doesn’t even care what it is that she’s shoveling in,” she said.Her father, Roger, also an actor, helped inform this bit. “My dad actually reminds me quite a lot of Mare, to be honest. He was slightly the inspiration,” she said. “He basically moves like Mare and eats like Mare. Well, he does eat with his mouth full. We do tell him all the time, ‘Dad!’ He’s going to be so mad I just said that.”Visiting the BadlandsAnd yet, Ms. Winslet, a vegetarian, could only get into character so much. She sheepishly confessed to a Philly sacrilege: The show’s hoagies contained no meat and, most shockingly, no onions. “I felt really, really bad because I know onions are a very important part of a hoagie,” she said, “but because we had so many hours of filming scenes with all of this food, it basically wasn’t fair on the crew to have all this stinky onion food on our tiny set all day long.” (She said she was aware of the existence of scrapple but did not try it.)“Her body posture is totally different to mine,” Ms. Winslet said of the character. “I actually stand quite upright.”Jamie Hawkesworth for The New York TimesEven with the counterfeit hoagies, locals are thrilled with Ms. Winslet’s metamorphosis. They even named a hoagie after Mare.Shawn McCreesh, who works with me at The Times and grew up, like the first lady, in a nearby town very similar to Easttown, spotted someone he recognized from back home on the show. Patsy Meck, who plays the woman working the desk at the police station, said that Ms. Winslet was “genuinely who you would want her to be — she was so real.” Ms. Meck, whose three grandchildren were extras on the show, said that it was “amazing” to see Ms. Winslet “walk off set, sit down and talk to me in a deep British accent, then pop right back on set and start talking like the rest of us.”Ms. Winslet said she had to change the way the muscles in her face moved — often in freezing weather — in order to emulate Philly’s mid-Atlantic dialect, with its selectively elongated vowels and smushed consonants. “Look, when you’ve done Polish-Armenian and German,” she said, referring to her accents in “Steve Jobs” and her Oscar-winning turn as a Nazi in “The Reader,” “frankly, I thought, ‘Delaware County, oh, it’ll be fine. The vowel sounds a little bit different, but it’ll be fine.’ Honestly, it was just so hard.”Still, mastering the sound wasn’t the hardest part. Stepping into the shoes of a mother raising a child with severe mental health issues, as Mare did, was. (Mare’s son, Kevin, had struggled with depression and addiction before taking his own life.) Ms. Winslet met with parents who had been through it all, and worked with a grief counselor.“There’s that moment,” she recalled, “when the therapist says to Mare, ‘Did he frighten you?’ and she just says, ‘Sometimes.’ A huge admission for Mare to even say out loud, ‘My son scared me.’ Of course, you see it in that flashback when Carrie and Kevin take Mare’s money for drugs in the bathroom.” She said the detective strives to fix everything else because she could not fix Kevin.In order to truly understand the opioid epidemic, how its many tendrils can wrap around a place like Easttown, she went to what Philadelphians call “the badlands” — the North Philly neighborhood of Kensington and its open-air drug markets. “We would go in an undercovery type of car and just drive around a lot,” she said.“I remember seeing — and actually it broke my heart — a man with the most beautiful face and a beard. You could see there was a soul right there. He had been amputated from the knee down on his right leg, and he was injecting into the toes of the other foot.“People are fighting for their sliver of life there. I would see people in these teeny-tiny houses, and they would be not just sweeping their front stoop but sweeping the pavement and the guttering in front of their home. Sometimes, for some people, that’s as much as they can do to keep their pride, to keep a feeling of something that is theirs and that is intact.”What did the dark heart of America’s opioid crisis look like to a Brit? “I have to be honest,” she said, “I was really staggered that there aren’t more of those support networks in place to help with people. In this country, we do definitely have better support networks for people in crises like that, we absolutely do.”‘Faces Are Beautiful’Ms. Winslet has been known to warn young actors on a set not to confuse social media fame with the hard work of acting.“I have certainly heard, twice, of certain actors being cast in roles because they have more followers,” she said. “I’ve actually heard people say, ‘She’s not who we wanted to cast, but she has more followers.’ I almost don’t know what to say. It’s so sad and so extraordinarily wrong. I think the danger is not just for young actors but younger people in general now. I think it makes you less present in your real life. Everyone is constantly taking photographs of their food and photographing themselves with filters.”She leans her face close to the camera, and noted her lack of filters, with an expletive.“What worries me is that faces are beautiful. Faces that change, that move, are beautiful faces, but we’ve stopped learning how to love those faces because we keep covering them up with filters now because of social media and anyone can photoshop themselves, and airbrush themselves, and so they do. In general, I would say I feel for this generation because I don’t see it stopping, I don’t see or feel it changing, and that just makes me sad because I hope that they aren’t missing out on being present in real life and not reaching for unattainable ideals.”The actress is so famous for disrobing in movies that her IMDb profile says her trademark is her “voluptuous figure.” But she says nude scenes may be in her past.“I think my days are getting a little bit numbered of doing nudity,” she said. “I’m just not that comfortable doing it anymore. It’s not even really an age thing, actually. There comes a point where people are going to go, ‘Oh, here she goes again.’” She jokes that it’s not fair to camera operators to have to work to get the best angles as her body changes.Ms. Winslet has a daughter, Mia, 20, with her first husband, Jim Threapleton, a director whom she met on the set of “Hideous Kinky.” She has a son, Joe, 17, with Sam Mendes, her second husband. And she also has a son, Bear, 7, with her current husband, who has gone back to his original name, Edward Abel Smith, from his playful pseudonym, Ned Rocknroll.“He added ‘Winslet’ as one of his middle names, just simply because the children have Winslet,” the actress said. “When we’re all traveling together, to all have that name on the passport makes life easier.” (Bear’s middle name is Blaze, after the fire that Kate and Ned escaped that burned down the British Virgin Islands home of Richard Branson, her husband’s uncle.)“He’s the superhot, superhuman, stay-at-home dad,” she said of her husband, as she smiled happily. “He looks after us, especially me. I said to him earlier, like, ‘Neddy, could you do something for me?’ He just went, ‘Anything.’” She swoons, noting that his long hair now gives him the look of “an ocean warrior.”She breaks into song, crooning that they go together like “shama lama ding dong.” “He is an absolutely extraordinary life partner,” she said. “I’m so, so, so lucky. For a man who is severely dyslexic, as he is, he’s great at testing me on lines. It’s so hard for him to read out loud, but he still does it.”She added that “He didn’t particularly plan on meeting and marrying a woman who is in the public eye and therefore having been so judged.” She finds it amusing that, instead of being rock ’n’ roll, he’s very Zen. “He’s vegan, does yoga, breath work and cold water swims.”Ms. Winslet grew up in Reading, west of London, in a modest house and worked slicing ham in a deli when she was young. “I came from a small community not dissimilar to Easttown in the sense that there were paper-thin walls,” she said. “You could hear the neighbors rowing through the wall. You could hear the verbal grenades that were being hurled at one another.”She said her father had called to tell her he loved an episode of “Mare,” then added his usual caution: “But you know, babes, don’t rest on your laurels. You’re only as good as your last gig.”Jamie Hawkesworth for The New York TimesConfirm or DenyMaureen Dowd: Bob Iger approached you about making “Titanic II” for Disney Plus.Kate Winslet: No, never did, and I never would.You pocketed a few things before you jumped ship from the set of “Titanic.”People stole the White Star Line cups and saucers. I was good. I did take a pair of Rose’s earrings, but somewhere I lost one.Like Mare, you have a gloriously filthy mouth in real life.(Laughs.) True, yes.You can’t stop reading about Ben Affleck and Jennifer Lopez.What? No! I’ve never read about Jennifer in my life. What are these questions?“Hideous Kinky” was neither hideous nor kinky.I don’t even know how to answer these questions.You keep your Oscar on the back of your toilet.I don’t actually know where the Oscar is at the moment. I think it’s possibly in my son’s bedroom. But it was on the back of the toilet for a long time, yes.You lived in New York for 10 years and never once went to Philly.That’s true.You’ve incorporated the Philly slang word “jawn” into your vocabulary.John, as in a man’s name?You went to Rita’s for wooder ice.No, I didn’t go to Rita’s.This role is the first time you held a gun, and you didn’t like it.True.In John Turturro’s “Romance & Cigarettes,” you simulated sex with James Gandolfini bouncing on an exercise ball.I had ripped all the ligaments on the left side of my foot. I’m nursing my son. As I’m bouncing on that ball, I’m actually bouncing using one foot with my leg in the cast improvising at three o’clock in the morning. We were in hysterics. Oh, God, I loved Jimmy Gandolfini so much. He was just so wonderful, so insecure and just so honest.Guy Pearce washes cans in the dishwasher before he puts them in the recycling can.That is true. More