Kate Winslet spent two years with the character of Mare Sheehan, a small town cop, mother and grandmother for HBO’s limited series “Mare of Easttown.” Becoming this woman wasn’t just about adopting a Delaware County accent, pulling her hair back into a ponytail, keeping her face free of makeup and never drinking water (look closely, Winslet says, it’s all coffee and beer) — although those were all essential elements for Winslet, too — it was also about tapping into a deep sense of grief and guilt over the loss of her character’s adult son to suicide. That’s why, months after wrapping production on the project, Winslet tells Variety she has felt a “huge crater” in her life, where Mare previously sat.

“We did have COVID cut right into the middle of our shoot, so in a way she almost became a bit of an alter ego for me — that was my coping mechanism,” Winslet explains. “People have done lots of different things through COVID to get through it. I was busy knitting the sweater of Mare the entire time.”

When the audience first meets Mare, she is busy raising a teenage daughter (Angourie Rice), as well as her young grandson (Izzy King). Her ex-husband (David Denman) is practically still living with her, and her mother (Jean Smart) is a stone’s throw away as well. The death of her son Kevin (Cody Kostro) still looms, but largest over Mare, who struggles with the mistakes she made in dealing with his mental illness, as well as concerns that her grandson has been passed those genetics.

“Mare’s backstory and her past was as equally important in its creation in playing her as the words that came out of my mouth on set every day,” Winslet says. “I couldn’t just show up and magically be it; I had to really find it and create it — to the point that my kids would be like, ‘Mom, Kevin’s not real,’ and I’d be like, ‘Shut up, shut up, shut up, shut up, shut up, shut up, shut up, he’s real, he’s real, he’s real.'”

Although much of “Mare of Easttown” follows Mare post-loss, flashback scenes between her and her son will further illuminate their relationship and some of the mistakes she feels she made. And Mare did make mistakes, Winslet previews: “She could have done better, she could have done things differently, so harboring that level of guilt and creating that and hanging on to it for the length of time I had to was really hard.”

“The actor Cody who plays Kevin, I couldn’t even look him in the eye. On the days he’d be on set, I would actually have to go and be in another room,” she continues. “It’s even hard to talk about actually, because I had to create the trauma and that grief — and the stockpiling and charging up of anguish that had to go on — to be able to manifest it.”

Winslet spent “a lot of time with grief therapists” to better understand the grief process, but she also spent time with families who lost children or other loved ones specifically to suicide. Working to understand “the true depths of mental illness” was invaluable preparation for the part, but that was only one piece of the role.

Mare’s work as a police officer takes her into the investigation of a teenage mom’s (Cailee Spaeny) murder. Since it is a small town, Mare knows everyone involved extremely well, and because another teenage girl’s disappearance is still unsolved, the pressure to close this case is heavy. An outsider detective (Evan Peters) comes in to assist, but ultimately, the weight is on Mare, who is “trying to live up to certain expectations,” Winslet says.

“It isn’t a thriller in that kind of dark, underbelly of a small town” way, she continues. “It’s just about people who fuck up and get things wrong — really wrong in some cases.”

That, of course, includes Mare, who Winslet says is “coarse and prickly, but she’s warm and deeply compassionate; she’s brilliant but she’s catastrophic; she’s morally sound and morally really unsound at the same time.”

She is also desperate at times, and out of that desperation will come a decision that is “profoundly wrong” and sends her to a “morally low point.”

“We’re very mindful not to abuse any degree of power in any other area, but to only give her that one moment that came from a place of desperation,” Winslet says. “Because Mare is not the person who I think, by nature, is an abuser of any power. And I actually think that she has tried all of her life to truly toe the line and be a good cop, in the way that I think her father was and would have hoped that she would be too.”

Whenever Winslet takes on such an immersive and complex role, leaving it behind is a matter of getting back to her regular time and “over time it disappears.” Thus far, though, Mare has perhaps lingered a little longer — and caused a greater emotional response when recalling certain pieces of her — and Winslet is now looking forward to sharing her with a wider group of people.

“I think once the show airs and is out there and people will be talking about it and hopefully excited to see the next episode with the great cliffhangers that we do have, I think then it will feel like it’s kind of taken away from me a bit more, which is obviously what I’m so excited about and can’t wait for,” she says.

“Mare of Easttown” premieres April 18 at 10 p.m. on HBO.