Natalie Portman and Todd Haynes discuss May December at Cannes

In Todd Haynes’ tonally shape-shifting May December, the first announcement of the movie’s playful intentions comes with a theatrical zoom in, a few lushly melodramatic piano notes and the frightful announcement that there no more hot dogs in the fridge.

That moment, which Haynes says signals “that there’s something coy happening in the language of the film”, is just a taste of what’s to come in May December, a delicious and disquieting drama laced with comedy and camp that Haynes premiered over the weekend at the Cannes Film Festival.

Natalie Portman stars as an actress researching a film that will dramatise a scandal from 20 years earlier.

She goes to Savannah, Georgia, in the US, to spend time with Gracie Atherton-Yoo (Julianne Moore), who years earlier become tabloid fodder for a sexual relationship with a young teenager.

Now she is seemingly happily married to him, Joe Yoo (Charles Melton), with children of their own and suburban barbecues to host.

The film, scripted by Samy Burch, takes a light but deliberate touch in navigating thorny themes of performance and identity. As Portman’s character grows increasingly like Gracie, ethical borders begin to tumble away.

“It was tonally such an amazing script and so rigorous,” Haynes said in an interview alongside Portman.

“It kept shifting the way you felt about or trusted one character versus another.

“That whole process as it manoeuvred through the course of the script was such a compelling experience. And I just thought wow, how could you translate into visually?”

May December, which Netflix acquired on Tuesday for a reported 11 million dollars (£9 million) with plans to release later this year, is the first time Haynes (who has regularly worked with Moore) has made a movie with Portman, 41.

For her, May December was a chance to not only work with a director she has long admired but explore some of her own fascinations.

“It poses a lot of the questions I’m most obsessed by about performance, about the purpose of art, about innocence,” says Portman, also a producer on the film.

“When you explore all those layers, playing someone who’s playing someone, making a movie of a movie in a movie, there’s so many layers of artifice, and what truth we can get out of artifice, which is the kind of alchemy of what we do,” adds Portman.

“We’re using lies to tell the truth, and it’s magic.”

May December has some unofficial roots in reality. Gracie is not very different in certain ways from Mary Kay Letourneau, a Washington State schoolteacher who went to prison after a relationship with a boy in her sixth-grade class.

Questions of identity and artifice have run through Haynes’ filmography, including the sumptuous 1950s romance Carol, the Douglas Sirk-inspired melodrama Far From Heaven, and his most recent film, the documentary The Velvet Underground.

In Portman, he found an actor who shared a similar approach to film.

“A lot of narrative filmmaking and fiction-making has an internal desire to redeem oneself through the process, to sort of affirm one’s own aims. That’s the thing that I’m not particularly interested in as a director,” says Haynes.

“And I’m drawn to actors who feel similarly, who are actually interested in creating a distance between maybe their own values and ideas and those portrayed in the character.”

He praised Portman’s eagerness to engage with “and lean into the most disquieting aspects of the character”.

Portman has famously played some real-life figures, like Jacqueline Kennedy (Jackie), which required copious amounts of research.

But in May December, she plays an actor far more reckless than herself. Yet even in a performance that could have easily slid into satire, Portman deftly inhabits her.

“Most artists who tell stories want to hold up their ethical standpoint in the light. It can be vampiric to take human emotion and human story and capitalise on it and tell a story,” Portman says.

“But hopefully the energy that you come to it with is empathy and the curiosity to explore someone’s human behaviour and someone’s inner self.

“That it’s an act of empathy and not an act of bloodsucking.”

There were long conversations with Haynes and Moore as they prepared to make May December in a 30-day shooting spring.

But unlike her character, Portman’s preparation for the part was mostly already done.

“Well,” Portman says smiling, “I’ve spent my whole life researching how to be an actress.”