Richard Curtis on How Melissa McCarthy's “Genie” Casting Mirrors Julia Roberts' for “Notting Hill” (Exclusive)

Writer Richard Curtis says he felt Melissa McCarthy was the "perfect" person to play the plucky Flora in 'Genie'

Richard Curtis struck casting gold once again with Genie.

Curtis — who wrote Genie, plus classic romantic comedies like Love Actually, Four Weddings and a Funeral and Bridget Jones's Diary — tells PEOPLE he "couldn't believe" he was able to nab Melissa McCarthy for the lead role. He says it reminds him of a time he was able to get exactly who he wanted for another film.

"I've actually got a photograph of me sitting in a chair receiving the phone call when Julia Roberts said yes to Notting Hill," says Curtis, 67. "Because we'd offered it to her and we thought, 'That's never going to happen.' And it was a bit the same with Melissa."

In the new holiday comedy directed by Sam Boyd, McCarthy, 53, plays Flora, a genie who is unwittingly summoned by down-on-his luck dad Bernard (Paapa Essiedu) during the yuletide season in New York City.

Bernard is struggling to connect with his family while under the thumb of his unrelenting boss (Alan Cumming, who originally starred as Bernard in Curtis' 1991 TV movie Bernard and the Genie, which the new film is based on), and enlists the help of Flora to untangle his mess.

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Related: Nicole Kidman Reveals She Wanted Julia Roberts' Role in Notting Hill: 'I Wasn't Talented Enough'

Curtis says he felt McCarthy was the "perfect" person to play the plucky Flora, to the point where they weren't really considering any other U.S.-based actresses.

"When she came straight back to us and said yes ... you don't know if people are going to be free, you don't know if they're going to say, 'I never want to make a Christmas movie.' So it was just such joy," he says. "And then getting into a room with her and her bouncing so many ideas."

"She's very respectful of the script, but also naughty with the script. So it was a catalog of delight," Curtis adds.

He says McCarthy has "such warmth" and is "such a fine actress" that she was able to strike the balance of Flora's playful nature and serious side perfectly — especially in one specific scene that comes with a big helping of deep human emotion.

Related: Melissa McCarthy's Best Movie and TV Roles

"I kind of knew always that was going to be the best scene in the movie, because she's got such sort of depth and tenderness to her," Curtis says.

Asked what lesson he'd want audiences to take from Genie, the writer notes that "in a funny way," the story "starts with the end of the movie."

"You can have all the wishes in the world, but do any of us like anything more than just sitting around a table with our family laughing? And that's meant to happen at Christmas," he says. "So in a way, the whole movie's a trick. It sort of says you can wish for anything, you can get anything, but in the end there's nothing better."

"I hope a lot of people watch it at Christmas and they're feeling those feelings that we're just lucky to be here sitting around a TV, enjoying a movie with the people we love," Curtis adds.

Genie debuts Wednesday on Peacock.

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