Halfway through our interview, Selma Blair’s one-eyed dog Buster climbs on to the restaurant table at the Chateau Marmont in LA and happily devours an entire plate of leafy greens. Strangers are staring. I’m staring. “Are you disgusted that I’m letting my dog do this?” Selma asks, her face serious, her tone as drily hilarious as it has been for the past hour, even when discussing the state of Hollywood for women and her fears that she’ll never work again. In fact, I’m just amazed that, here in Hollywood, even rescue mutts with part of their face missing seem to enjoy rocket salad with a blue cheese dressing. “I wonder if it’s possible to overdose on arugula?” she thinks aloud. “We’ll see when the dog dies tonight.”

Blair made her name with Cruel Intentions, a 1999 mean-teen remake of Dangerous Liaisons, and has since acted in Legally Blonde, the Hellboy films directed by Guillermo del Toro and in the US remake of Kath & Kim, where she played the hysterically funny and spoiled daughter. More recently she played Kris Jenner in an episode of American Crime Story. Now she’s in a comedy-ish horror film called Mom and Dad, which isn’t going down too well in America, what with its theme of parents overtaken by the urge to murder their own children, though Blair’s performance has been praised by the Hollywood Reporter, which describes her as a “chronically underused talent”. Nicolas Cage plays her husband, and they spend half the movie trying to end their two kids with an assortment of homemade weaponry.

“I happen to love it,” she admits, “because I had such a good time on it, laughing. It was funny to me. Isn’t that terrible? I can’t bear horror movies usually – my mom took me to see American Werewolf in London as a kid and I couldn’t be alone for two years after that, not even to tie my shoelace. So I would have said a film like this doesn’t help anybody, we have enough problems with killing. But then there was something so refreshing to me about saying, aaaah, fuck it all! And the premise is so much more horrible than the film itself.”

Her real son Arthur came out to the location and played with her son from the film. “He was really taken with Zach [her son in the film, Zachary Arthur], he was like: ‘I finally have a brother!’ I was like: ‘Er, not real, and I’m trying to kill him?’ He hasn’t seen the film, but when he misbehaves I’ll show him.” Also coming out soon is a remake of Heathers, in which it’s not the traditionally beautiful girls who run the school at all, but the outsiders who’ve taken over. Blair, who rose to fame as part of the young Hollywood of the original Heathers generation, is now 45 years old, and plays “a diabolical stepmother who turns out to be the only sane person in it, because she’s the one who gave zero fucks and didn’t have a conscience to begin with”.

‘I’ve been in love, I’ve been in lust, I’ve been crazy about someone’: Selma wears jacket by Coach 1941 x Keith Haring, dress and T-shirt both by Coach 1941, and shoes by Christian Louboutin. Photograph: Dylan Coulter/The Observer

Blair grew up in Michigan, one of four sisters in a Jewish family. Her parents were both lawyers – her mother a judge – and they sent her to Cranbrook Kingswood, a private school that Blair speaks about with great affection. Yoko Ono was a guest; Keith Haring designed their yearbooks, and Blair still has her best friends from there because, apparently: “It wasn’t cliquey, there were no mean girls. It’s still one of the most beautiful places I’ve ever seen.” She remembers the glamour of her mother power-dressing in Ungaro suits, with “the looks of Sofia Loren”, and also the formalities. “She had us all by C-Section at 8.45am on a Friday so she could be back to work by Monday.”

Blair began acting at school and, after encouragement from a teacher and various TV and film parts, her breakout role was in Cruel Intentions, a film she now describes as “pioneering for teens. It was the first time two girls kissed onscreen in such a mainstream movie.” She was actually 25, but playing a 14-year-old, “because this was before HD so you could still look somewhat young on screen”.

Yet her early 20s in Hollywood were not easy. In the wake of the accusations against Harvey Weinstein, Blair spoke to Vanity Fair alongside Rachel McAdams about another big Hollywood figure, the director James Toback. She was told he wanted a meeting with her, but then, like Weinstein, he insisted the meeting be conducted in his hotel room, where he became manipulative, trying to convince her he could only fully coach her as an actor if he saw how she used her naked body, and then trying to block her from leaving the room until he ejaculated on her because he “needed his release”.

At the time Blair was estranged from her father after her parents’ divorce, and she says Toback said he could have him killed, because he worked with contract killers. She says Toback also threatened Blair’s own life. She was terrified and felt it was safer to go along with his sexual demands.

“I said recently that once I had said it, I let it go completely. But I didn’t let it go completely. I let go of the shame. And I was ashamed for being a part of it, like how could I not hit him over the head and run out of the room? But I could let that go when other women told their story to me. I thought, well, this was a natural reaction for that time.”

‘Cruel Intentions was pioneering for teens. It was the first time two girls kissed in such a mainstream movie’: Selma wears dress by Erdem. Photograph: Dylan Coulter/The Observer

At first, she says, she was too frightened he would sue her. “So we women assembled behind the scenes on Twitter and I was saying in DMs [direct messages], go to this reporter, go to this reporter. But I was still afraid because I was the only one who was somewhat known, so I thought this is all gonna be on me, this lawsuit. I won’t be able to put my kid through school. Then it turned out there were 38 other women accusing him, and he called them cunts and cocksuckers and liars, so I thought, OK, I’ll lose everything, I’ll go to court. I will be on the right side of history. Now he’s up to 396 women, and I’m sure there are thousands. I also know plenty who haven’t come out, because what he did to them was so horrifying. He has yet to speak again of it.”

So what happens next? Why isn’t he in jail? “Oh, he gets to just hide. I filed a police report, but there is a statute of limitations. He won’t work again, but he’ll never really be held accountable, even though he should be in a mental hospital and a jail.”

Blair is now the single mother of six-year-old Arthur, her son with her ex-boyfriend Jason Bleick, a fashion designer. She texts her babysitter during our lunch, hoping that her beloved boy can join her here at Chateau Marmont, where the staff like her so much that she has a much sought after key to the locked swimming pool. “It’s my only Hollywood perk, literally my only one after 20 years. They treat Arthur like the Prince of the Chateau.”

She and her son love animals and she goes riding at 6am as often as she can. She scrolls through her phone to find me a picture of their horse, muttering: “Why am I doing this to you? Why am I forcing this picture on you?” She never planned to get pregnant, and wasn’t married. “But my body felt good and I felt happy. And I’m not necessarily, historically, engineered that way,” she adds, meaning she has been prone to melancholy all her life. “So I was, like, maybe it’ll change me forever!” And has it? “You know what’s weird?” she asks. “Your DNA changes and you get your child’s DNA inside you, because cells from the foetus cross the placenta. And because some of your child’s DNA is the other person’s, you get their DNA, too.”

Having bonded over the fact that we are both single mothers of unplanned six-year-olds, we now sit and think about our bodies containing parts of our ex-boyfriends forever. There is a loaded silence. Blair had a bad, induced labour and a rough time afterwards, not sleeping, lacking support. One friend would come and cook for her on Sundays, but otherwise she thinks she became malnourished. (All new mothers talk about the lack of sleep. Single mothers talk about the lack of food.) Yet she managed to breastfeed not for months but for years, “because I’ve always been someone that could make milk, ever since I was seven years old. Never had breasts, always had milk!”

‘I’d be content if I could just ride horses all day’: Selma wears dress by Alexander McQueen and shoes by Christian Louboutin. Photograph: Dylan Coulter/The Observer

My jaw drops again. What? Turns out she has the rare condition idiopathic hyperprolactinaemia, which can lead to galactorrhea, in which the nipples emit a discharge resembling milk. An Ayurvedic healer once told her she was producing this “because I had never loved anybody, and this was my spirit trying to bring that person to me, to be loved”. Though Blair looks like someone who’d laugh in the face of hippy healing ideas, this really resonated with her. “I was about 34. And I thought, maybe that’s right, I’ve never loved somebody unconditionally – I’ve been in love, I’ve been in lust, I’ve been crazy about someone, but I’ve never really still… no. It rang true.” This was after her two-year marriage to Frank Zappa’s son Ahmet had ended. “And then my son had some health issues and he really needed the breast milk, so that really was my job. I thought: ‘Aaaah, I guess I can die now, I got him through that!’ But I depleted myself, too, and I’m still recovering. I still have to remind myself that my own body needs healthier fats than fried food.”

She recently bought the film rights to a novel she loved, The Lost by Sarah Beth Durst, which is about a woman who has been caring for her sick mother for years, but one day just gets in her car and drives, only to end up in a mysterious town where nothing grows and everything has been lost and discarded from elsewhere. “It was so simple, but also metaphysical and magic. It really lifted a veil in my mind. There are so many women to play, so much room for them.” So she wrote the proposal and is now pitching it, with her as producer and possibly as the lead. She has no other work lined up “and it feels like my only salvation. I had to do this.”

But then she started talking to men in meetings about it. “They just sit like lumps, going: ‘I don’t want to like this character because she left her mother.’ Well, one, she left her mother for a drive, and two, you can’t like a woman who’s broken her back to take care of other people her whole life? You’re not gonna follow this heroine?

“Once I had my child, I realised how unfair life has been for women. When you deal with potential custody issues, which we ended up not having, but you look into it and realise this is all geared towards men now, and the court systems usually loathe single mothers. I thought, I do not have this fight in me, I don’t know how to deal with this. We’re too powerful, so we dim our shine to get through stuff. I didn’t even realise until people started speaking up how really kind of… furious… we should be allowed to be.”

I feel like this could be 10 years of rage. “Yeah, this is just the start. It starts with stories and then how do you change the system, how do you change the lesser aggressors, the ones who shouldn’t be criminalised, but how do we teach our children no, you get out of the room, you have that right. And not have the consequences be so scary.”

I ask if it’s right that women are carrying this whole movement: should men be helping more? She responds that it was another male Hollywood director who encouraged her to speak up about Toback. “And the men who are trying to change themselves and be better people every day… Fuck, I love them! Even the assholes. If they could just own some of it. How far it would go to healing some people if they could just say: ‘I did it.’ Louis CK – even if he was cornered into saying it, and it doesn’t make everything right, but saying: ‘I belittled people, I did much worse,’ well, that does something. So I hope I raise a son who wants to be a better person every day.”

In the meantime, she needs to make some money. I say she seems like she doesn’t want to join the Hollywood club. She agrees. “I probably need to look like I’m trying to join the club. It’s true, there wasn’t a desperation before, but with a kid I’m being introduced to some desperation. I’ve never made tons of money, I’ve never been a huge star. I’ve always been the dark horse.”

Surely this goes in your favour, too? She cheers up and admits that it can. “It’s true, I’m not totally out because I’ve never been totally in. There’s a certain luck I have because people think I’m still chic, because I never wanted to be totally in. For me it’s about survival. I’d be content if I could ride horses all day and be with my son and read books. I’m kind of simple. But I have to make a living and I’m a bit scared shitless how I’m gonna do this.”

The other people I interview never admit that. “Well, maybe the other people you interview aren’t scared shitless. Could someone pay me for an Instagram post? How do all these people do it? I would be very happy to shill something I liked!” Such as what, I ask? “Well, I don’t know what my market is,” she replies, “but maybe the Salad Association would like my dog.”

Mom and Dad is in cinemas from 9 March

Styling by Gaelle Paul and Hope Lawrie. Hair by Anh Co Tran, L’Oréal ambassador at Tracey Mattingly. Make-up by Kathy Jeung at Forward artists using NARS. Shot at Quixote Studio