The daredevil couple behind the Oscar-winning doco Free Solo

Alex Honnold peers over the edge of Glacier Point in Yosemite National Park. Photo / National Geographic/Jimmy Chin

The focus on the spatula was, she admits, principally her idea. "I just thought it was really funny," laughs the film-maker Elisabeth Chai Vasarhelyi. "This guy, climbing rock walls without ropes or harnesses, then dating on the Internet, living in a van ['dirtbagging' as the off-the-grid lifestyle is known] and eating straight out of the saucepan with a spatula.

"It's very efficient," she adds, equably. "It's the way we all secretly want to eat, but we don't feel we can."

That spatula is now part of an Oscar-winning film; last month, 39-year-old Vasarhelyi and her husband and film-making partner Jimmy Chin, 45, won the Academy Award for Best Documentary Feature for Free Solo, which follows the superstar climber - and proud spatula-owner - Alex Honnold and his attempt, in June 2017, to become the first person to climb El Capitan 'free solo': without the use of ropes or harnesses, using only his fingers and feet to grip on to the 1000m granite wall. Honnold summited El Cap, as it is known, in three hours and 56 minutes - a feat which the New York Times described as 'one of the great athletic feats of any kind, ever'. The first team to ever climb it, in 1958, took 46 days.

Jimmy Chin and Chai Vasarhelyi on location during the filming of Free Solo. Photo / National Geographic/Chris Figenshau

Chin - a fellow climber as well as a photographer and film-maker - and 34-year-old Honnold had been friends for over a decade. "At first, the film was just going to be a character portrait of this person who loved to climb without ropes, and we'd look at why on earth someone would ever climb without ropes," says Chin.

Then, Honnold confessed to Vasarhelyi that he wanted to free solo "El Cap", the notorious wall in California's Yosemite National Park, considered one of the most difficult climbs in the world. Suddenly, the film was a very different proposition. "My initial reaction was that I didn't want to do it – it was too dangerous," says Chin. "But the conclusion that I came to eventually was that if anybody could do it, it was going to be Alex."

I meet the couple in the 53rd-floor penthouse of a Manhattan hotel, surrounded by skyscrapers. Vasarhelyi grew up just across Central Park, on New York's well-heeled Upper East Side. The daughter of intellectuals who emigrated to the US from Hong Kong and Hungary - her father is a business professor at Rutgers University, while her mother is CFO of the prestigious design institution The New School – she attended Brearley private school, then Princeton University. She made her first documentary, about the Bosnian conflict, aged just 24.

Alex Honnold, at Glacier Point in Yosemite National Park. Photo / National Geographic/Jimmy Chin)

Chin, meanwhile, grew up in Minnesota, where his parents were librarians. "I read a lot, and my imagination would run wild. As a kid, I was always dreaming of being in these exotic, crazy places," he says. At 17, he fell in love with climbing, which, he says, "felt like a very physical but also a cerebral sport." After graduating, he started climbing full-time, discovering photography as a means to support himself. He has since led expeditions in China, Pakistan, Nepal, Tanzania, Chad, Mali, South Africa, Borneo, India and Argentina, was almost killed in an avalanche while attempting to climb Everest in 2003, and was part of the first American team to ski down the same mountain in 2006.

Vasarhelyi, she makes very clear, does not climb. "I'd much rather go to yoga," she quips. But she is a top-class skier; her father taught her to ski in Jackson Hole, Wyoming from the time she was 3 years old. "So my relationship to mountains has to do with skiing, and that's something Jimmy and I can do together – it's a really great part of our relationship," she enthuses.

The couple first met in 2012, at an ideas conference near Lake Tahoe, California, where Chin was giving a talk about failure. In 2008, along with fellow climbers Conrad Anker and Renan Ozturk, he attempted to climb Shark's Fin, a 1219m wall in the Himalayas, but the group turned back 300m from the top. They returned in 2011 and successfully summited, with Chin also filming the expedition. Vasarhelyi was already a noted film-maker, having made award-winning documentaries such as Incorruptible, her 2012 film about the Senegalese presidential elections. After their meeting at the conference, Chin sent her his footage from Shark's Fin, and asked for her help in making it into a film.

"I was shooting another film in Africa, so it took me a long time to watch the footage," she admits. "But when I did, it was fantastic. It's the type of material that compels you – it felt Shakespearian, and it just had to be made." Three months later, when she returned to the US, they began working on the film - and dating. "Clearly my love of the material probably had something to do with my love for him," she reasons. They married a year later, and the resulting film, Meru, was shortlisted for an Oscar in 2016.

The couple now have two young children and split their time between New York City and Jackson Hole. Has Chin's approach to risk changed since becoming a father, I ask. "I think that shift actually happened before I had kids – and that allowed me to even think about having kids," he says.

Rock climber Alex Honnold.

Nevertheless, the filming of Free Solo was an undertaking almost as ambitious as Honnold's climb itself, with Chin and a four-strong team of climbers-cum-cameramen suspended on the wall, plus a helicopter, while attempting to be unobtrusive. As they have acknowledged, they were "haunted by the possibility that our presence might put him at more risk every time we turned on the cameras."

"Filming an NBA player, they could lose the game, people would see them drop the ball, but it's not like they're going to die," says Chin. With Free Solo, however, that was a very real risk. "And with the vérité aspect of the film, we were sitting there in the van with Alex - someone who is very uncomfortable with intimacy – and asking him all about his feelings," says Vasarhelyi. "So that was also a big concern of ours – are we tinkering too much in his head?"

Honnold's amazing feat and the film's incredible success both confirm that this was, in fact, very far from the case. But, says Chin, that doesn't mean they want to push their luck. "We have some new ideas cooking," he says. "But we're definitely not making Free Solo 2."

Free Solo, Sunday 10 March, 7.30pm, National Geographic. Also available on Sky Go and Sky On Demand.