‘The movie is to be eaten alive and re-metabolised and shat out differently, from everyone’s perspective,” says Kristen Stewart, bracingly. The actor’s directorial debut, The Chronology of Water, has been doing the rounds at film festivals, and when we meet in London the reviews are coming in. Stewart knows that this impressionistic, arthouse collage of a film – adapted from an experimental memoir about a woman’s pain and loss, the elusive nature of memory and the reclamation of desire – is not going to be for everyone. “My favourite Letterboxd review is: ‘The Chronology of what the fuck did I just watch?’” But it matters to her that people respond to it. “Whether it’s your least favourite movie or your most favourite, it’s not lying, it’s genuine. And I’m so fucking proud of that.”

Stewart is sitting next to the film’s star, a slightly more sanguine Imogen Poots. Watching Stewart talk, her leg bouncing, her vocabulary ferocious, feels a bit like being sandblasted. It is invigorating and strangely galvanising, but you don’t go into a conversation with her half asleep. The same can be said for the film itself. “Language is a metaphor for experience,” writes the author Lidia Yuknavitch, at the beginning of the book on which it is based. “It’s as arbitrary as this mass of chaotic images we call memory.”

Stewart first read the book in 2018, while on the set of the movie JT LeRoy. She saw the visual potential in this mass of chaotic images and quickly decided it would be her first feature-length film as director. “Forty pages in, I was so rallied and so viciously adamant that nobody else could make the movie but me,” she says. “It was so physical. So vital. Such a permeating secret. There’s an unearthing quality to the way that [Yuknavitch] talked about trespass, and how your desires are carved into your body. As a woman, we have these seeping birthplaces that are our orifices, and it’s where we hold our power, but it’s also where we’re taken advantage of.” At this point, less than two minutes in, it’s fair to say that it isn’t quite turning out to be your run-of-the-mill movie-star promotional chat. “We’re all so muzzled,” Stewart says. “And it just felt like the muzzle was off. That’s the fun part. It’s got a loud mouth. A big, wide-open mouth.” So she sent Yuknavitch an email.

“A wildly exciting email,” the author says, from her home in Portland, Oregon. “She was explaining to me why I could never let this book be a regular biopic movie, and how I had to let her make a piece of art out of it. The language she used went under my skin immediately, because it wasn’t regular-person language.” Yuknavitch, obsessed with films since she was five, was, of course, familiar with Stewart’s work. “I even wrote a novel with her in mind, a while ago. She was younger. She had just punched through the Twilight experiences, and she was moving toward independent art films, and I pictured her in my brain when I wrote this novel.” It is called Dora: A Headcase. It sounds like a spooky connection, if she believes in that kind of thing? Artists, Yuknavitch replies, have a tendency to find each other. “They run across each other’s work, and these threads or streams we don’t entirely understand touch each other. And I think that’s what happened.”

It was not an easy film to finance. Poots and Stewart, both big readers, get into a meaty discussion about how confessional literature is taken seriously when men write it, and “belittled, constantly”, Stewart says, when it comes from women. “There are so many examples within modern literature of men laying it all bare, but as soon as you do something overtly personal as a woman, it’s less serious,” Stewart continues. “We’ve just been fully X-ed out of modernism in the canon. It’s like we don’t exist in it whatsoever. And it’s such a fucking crock of shit. You have to be Virginia Woolf to be considered a good writer.” Reese’s Book Club, this is not.

Did they come up against those attitudes when making the film? “Yes, because I think when people read it, it was reduced to how to sell it,” says Stewart. “OK, well, what’s it about, incest and rape? Fun!” It was not an easy pitch, she admits. “It’s about the gouging out of desire, and the reframing of that, and how empowered that is. In a slug line, it’s a really tough sell.” It took eight years of development before they finally got to work, mostly on location in Latvia. In the meantime, Stewart continued to act, and directed smaller projects: a couple of short films and a music video, for the band Boygenius. Chronology ticked away in the background, sometimes unpromisingly, until eventually it somehow came together. Even Stewart’s longtime producer, Charles Gillibert (On the Road, Personal Shopper), had told her that he couldn’t finish the script. “And he’s not the only one. He really encouraged me not to make this movie,” she smiles. “I was like: we’re gonna cease being friends if you keep saying this to me.”

Poots plays the adult Lidia with bodily gusto. The film is a collection of fluids and fragments. Poots read Stewart’s screenplay, and then the book, and then sent Stewart “a really pretentious email, which she lapped up”, she teases. Was she nervous about taking on a role that is so stark and exposing? It pulses with sex and drugs and violence. Bleeding and sobbing and grief wash over it. “Any actress I know would have wanted to play this part,” says Poots. In fact, she explains, casting her as the lead meant that the film was harder to make. “If Kristen had hired a massive movie star, then it would have made getting the money a hell of a lot easier,” she says.

Poots is a best-kept-secret kind of actor, and her performance here is immense, but I ask Stewart why she felt so loyal to her. “She’s my favourite actor, and everyone else sucked,” she shrugs. “There was literally no one else, and she’s been a fave of mine for ever.”

“And we have the same teeth,” says Poots, showing them off.

Stewart flashes hers in unison. “Because we have the same teeth, I thought: this is my girl. Bucktooth!”

The film also stars Kim Gordon, Thora Birch and Jim Belushi, who plays the late One Flew Over the Cuckoo’s Nest author Ken Kesey. It is a merry band of misfits. “What’s really cool, and you wouldn’t have been aware of it, is that these people, who have all been at the centre of these incredibly creative community movements, wanted in on what you were doing,” says Poots to Stewart.

Did she pull in any favours to get them involved? “Nobody did me any favours, trust me,” Stewart says, gravely. “In fact, we got fucked. In the face. Over and over.” She pauses. “Like a real woman!” she jokes. To be honest, she says, Belushi came on board after a couple of other actors dropped out. “I don’t think it was an easy yes. But the feeling of him supporting you, a nice pat on the back from Jim Belushi, could make you cry. He’s kind of a radical, and he’s a hippy, and he was perfect to play this part.”

As the film deals in memories, it rejects any sort of conventional narrative structure. Men come in and out of Lidia’s life, which meant that actors would come on set briefly and leave again, “sort of like a conveyor belt”, says Poots.

“Or chapters,” suggests Stewart.

“These insanely brilliant, talented actors,” says Poots.

“And they serviced you,” grins Stewart. “It was fucking incredible to watch male actors come in and have it not be about them. I would be like: sorry, but we’re actually not gonna shoot you. We’re just gonna shoot her. But talk to her. You’re here, kind of, but this is about her.”

Poots cackles. I’m guessing this is not a typical experience? “Mmmm,” says Poots. “For so many reasons.” Both say they plan to make “a lot more movies” together.

A few weeks later, Birch video calls from her home in Los Angeles, her dog lounging happily in the background. “You cannot enter a conversation with Kristen Stewart without coming locked, loaded and ready to go,” she laughs. “It’s intimidating!” Birch plays Lidia’s older sister, Claudia, in a brief but mighty role. In one of the film’s earliest scenes, she holds a sobbing, grief-racked Poots in the bath, following the death of Lidia’s stillborn baby girl. “Imogen is just a knock-down, one-two-punch, hazelnut-popping actress out of the Brit academy if I ever saw it,” Birch says, brilliantly.

Birch and Stewart had met at an event where they did some “mutual fangirling”. A few months later, Stewart called and said she was making a movie. Birch signed on straight away, and then she read the script. “I’m not going to lie, it was a little bit of a daunting process,” she says. “But I just trusted her already.” Partly, she thinks, that’s because they have some shared experiences. Both became famous as children. Stewart was 12 when she starred in Panic Room, while Birch’s run of 1990s and early 2000s films – from Hocus Pocus to Now and Then to Ghost World – defined adolescence for a whole generation of girls.

“Maybe I related to her because we’re both performers who started out very, very young, and so we had a common language. I say she’s my spirit animal. She does a lot of things that I do, but just way better,” Birch says. She had followed Stewart’s career from afar. “Different times, different generations, but the way she handled [getting famous young], I was just like: dude, that’s with aplomb. You knocked it out of the park, because you held on to your individuality and your point of view, which can really be difficult to hold on to.” She waves a hand. “But let’s not get too far into that.”

In its boldness and experimental form, The Chronology of Water may well be a surprise to those more familiar with Stewart, the movie star, who might not expect a film like this from her. “I sort of did,” counters Birch. “This is a very Kristen Stewart movie.”

She is glad, she says, that this is the story Stewart chose to tell. “She will hate me for saying it, but I’m sorry, this is emblematic of a female experience that not a lot of people are ready, willing or even able to dissect and talk about.” The movie covers some “heavy shit”, Birch says. “We’re talking about period blood and stillborns and familial sexual abuse. Nobody wants to talk about this stuff, and yet she presents it in such a way that it marries fantasy and poeticism, and but also the human experience. It’s a punk rock arthouse movie that is like a non-psychedelic ayahuasca trip.”

It makes sense, then, that Birch had no idea how it would turn out. She just had to have faith in what they were doing. “And then when I saw it, I was like: oh, that’s what she’s doing. One reviewer said: homegirl can direct. And coming from LA, I was like: yeah, that’s it. Homegirl can direct. She knows what’s up.”

• The Chronology of Water is released in UK cinemas on 6 February