But with the arrival of a mysterious man from her past (Stephan James), she begins to realise that she is not being told the truth of what happened to her – or even who she is.

“It reminded me of Big Little Lies,” Witherspoon, 46, says of the script. “It’s this very affluent community, but there’s this mystery lying underneath it all. It’s unsettling, and as an audience member, you don’t know who to trust.”

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The British actress was drawn to the challenge of playing a character like Sophie who is essentially a “clean slate”, with a backstory that only becomes more apparent as the eight-episode first season progresses.

“It was an interesting place to start, to feel like I was building Sophie as the audience was experiencing her too,” Mbatha-Raw says. “One of the essential questions of the show that I found fascinating was, ‘Is it generous to protect people from the murky things about their history, or is it actually a selfish act?’ There was lots to chew on.”

Although Mbatha-Raw, 39, has acted professionally for 17 years in films such as Fast Color and Beyond the Lights, Surface marks her first time producing. She credits Witherspoon and her production company, Hello Sunshine, for inviting her to the table.

Witherspoon “certainly walks the talk, in terms of empowering women”, Mbatha-Raw says. “I’ve been working for a bit now and have picked up so much along the way, so this was really a chance to develop my voice.”

Frustrated with the roles she was offered after her Oscar-winning performance in 2005’s Walk the Line, Witherspoon turbocharged her career nearly a decade ago as a producer, shepherding female-centric projects.

“We’re just making up for lost time,” Witherspoon says. “There were so many times in my career [when] I wasn’t invited into the decision-making process; I was told where to be, how to be and what the result would be.”

A turning point was the 2014 drama Wild, for which she earned her second best actress Oscar nomination, playing writer Cheryl Strayed. Strayed sent Witherspoon an advance copy of her 2012 memoir, which the actress shopped around to studios.

“I said, ‘I’m not changing a word. I want her full spectrum of a female experience to be on film, and I don’t want it neutered’,” Witherspoon says. “It’s a movie that changed my life: developing the film, having it actually happen and then watching audiences receive it was one of the most important, formative experiences of my career.”

That movie’s success “makes me feel like people are hungry for genuine, authentic storytelling with women at the centre”, Witherspoon says. “I mean, we’re 50 per cent of the population, but not represented in as many films. And it’s a good message to our industry, too, to make more films like this.”

Looking ahead, Witherspoon has more than a dozen projects in various stages of development as a producer and actress, including one she says she “can’t really talk about”, in which she is “reprising a character I played a long time ago”.

There is also a third Legally Blonde movie on tap, co-written by Mindy Kaling and Dan Goor.

“So definitely that gave us a lot of inspiration about what we would want to do with Elle Woods and make sure that we had all those same touchstones that mattered to people [back] then.

“I feel like these characters are my friends, so I safeguard them. I would never make the subpar, mediocre version of their story.”