"I have no problem talking about how hard it's been, how broke I've been and how broke I was not even that long ago," Larson says. "I was freaking out around this time last year because I thought, 'This is it. I've really screwed myself because I did three independent films. I didn't do anything for money and now I don't have anything.' I was eBaying stuff for Christmas presents."
What about the Oscar buzz for Short Term 12? "The first time I heard that I laughed and said, 'That doesn't happen to real people!"' she snorts. "This is so grand: if we were talking about a multimillion-dollar movie, if I was in Les Mis, I'd know what I was signing up for. But I'm a frickin' child just knocking around, tripping as I get out of bed. So it's strange. It's," she takes a long pause, "generous."
Short Term 12 is certainly not Les Miserables. Larson plays Grace, one of the supervisors in a foster home for volatile, at-risk children in California. The writer-director, Destin Daniel Cretton, worked in a similar institution for a few years in the early 2000s, and Short Term 12 is shot in a real facility, which was in use for 17 years before the authorities ran out of funds. These details lend the action a documentary feel: as the kids act out, and Grace attempts to exercise control, it often makes uncomfortably real viewing, though Cretton throws in enough humour and hope for the film not to be overwhelmingly bleak.
"It was the best script I ever read," says Larson. "Most people think at least half of it is improvised or documentary. They don't realise that every word is exactly as it's written. It's just incredible what Destin did. The brilliance of Short Term is that you feel you're watching a very fluid day-to-day experience." Larson is the emotional heart of the film, and her Grace is tough and independent yet damaged and vulnerable - if there is a lesson in the film, it's that carers are often as fragile as the children they look after.
In a stand-out scene, Grace takes out her frustrations on the car windscreen with a baseball bat. It is a cathartic moment to watch and it turns out to have been an empowering one to perform - albeit with the stress that, given the film's micro-budget, Larson had just one chance to get it right.
"I had this weird, instinctual, animalistic thing come over me," she recalls. "I've never smashed anything in my life but that first crack of the windshield, it was like something turned in me: I was only supposed to hit it three times, but I must have hit it 20 or 30 times and it just felt better and better the more I kept going into it. It summed it all up for everybody: we were this small crew of people and we weren't there for our paycheck because there wasn't one. When they yelled 'Cut!' it was like, 'Yeah!' It was the Super Bowl, it was so exciting."
Larson, who shadowed a care worker in LA before starting the film, admits that decompressing was problematic during the 20-day shoot for Short Term 12. Her coping mechanism was an unexpected one: she would design typefaces. It's been a hobby since she was in her teens; her all-time favourite is a type she created where every letter resembles a 3D mouse hole.
"I made three or four different fonts during Short Term 12 - it was how I'd calm my mind between scenes," she says. "I have graph paper and gel pens and I would do the alphabet: just do 'A' over and over again until I got it perfect and then go to 'B' and then 'C'. I definitely look like a weirdo with scraps of paper everywhere. But I can't read a book and then jump into this character, so it ends up being the perfect thing for me: it keeps my mind active and you get something at the end." Larson was home-schooled for much of her childhood and graduated from high school aged 15 - a year before she released her debut pop album, Finally Out of PE. Meanwhile, a pattern was emerging with Larson's acting career: "I'd hit the point where I'd go, 'Okay, that's it. That's the last dollar. I've got to quit or go to college or whatever.' But that day or the next day, something would happen that would make it strangely apparent I'm supposed to keep doing this a bit longer. It's never failed that the second I hit the last dollar, something turns around." In recent times, Larson has been saved by the United States of Tara, the Showtime TV drama starring Toni Collette, and Scott Pilgrim, which she describes as "a big life-changer for me".
She can also be seen in Joseph Gordon-Levitt's directorial debut, Don Jon. Larson also writes and directs her own short films: her first, The Arm, won the jury prize at Sundance. She wants to release a new EP of music and play some live gigs this year, too.
But Larson is not getting carried away. "This is nice for a moment.
"Maybe it goes away, but this is the way I've chosen to live: I want to go down or rise up as an artist. I don't want to get swept up in lipstick or whatever the hell."
Who: Brie Larson
What: Short Term 12
When and where: Opens at cinemas on January 9
- TimeOut, Observer
