Michelle Williams as Marilyn Monroe? Kenneth Branagh as Laurence Olivier? Doesn’t sound right, does it? In the first case, casting the gamine Blue Valentine star as history’s most famous pneumatic bombshell seems utterly inappropriate. And hiring Britain’s overhyped “new Olivier” to play the old one is simply too obvious, right?

But that’s exactly what Brit director Simon Curtis did for My Week With Marilyn, and, dammit, it actually works. For those among us who feel that Branagh’s lustre began to seriously fade around the time of Woody Allen’s Celebrity, his performance as Sir Larry is outrageously good fun, being as microscopically well observed as you’d expect. But it’s spiked with a certain knowingness, as if Branagh is winking at the audience a little.

“It felt bold but perfect,” says Curtis, speaking to the Straight from a hotel room in Toronto. “You could say that I gained from the fact that it felt like a part that’s been marinating for two or three decades. He’s a supremely good actor.”

He certainly is, and he’s also occasionally annoying. Not this time, though. As for Williams, critics have rightly lined up to praise the rising American star for a turn that isn’t an impression so much as a convincing meditation on Monroe’s crippling vulnerabilities. My Week With Marilyn is based on Colin Clark’s memoirs recounting his time as Olivier’s assistant on the tortured production of The Prince and the Showgirl and his brief relationship with Monroe.

“This is Marilyn age 30, and Michelle just brings such psychological texture and complexity to the table. I knew that was the Marilyn I wanted to see,” Curtis says. “And, you know, Michelle had a brilliant insight that in her Method way, Marilyn was interested in Colin because in the film The Prince and the Showgirl, Marilyn had an interest in the young prince in the embassy. I thought, ‘Wow, that makes sense.’ ”

What Williams achieves is just the right amount of weight in a film that’s mostly confection. Among its other incidental pleasures is Dame Judi Dench as a warm and maternal Dame Sybil Thorndyke (Curtis describes Dench as being, similarly, “a sort of kind, wise presence on-set”), as well as the loving re-creation of Pinewood Studios in the ’50s. And for eagle-eyed ex-pats, there’s the brief appearance of Norman Wisdom. His fame never travelled abroad, but Wisdom was a household name in the U.K.

“The weird thing, on the day we were re-creating Norman Wisdom in his heyday at Pinewood, that was the day he died,” Curtis recalls. “It was the kind of thing that was happening all the time on this film, the echoes of history sort of knocking into us. We filmed on various sound stages [at Pinewood], some of which were the same. We were doing the first make-up test with Michelle and they said: ‘We’ve given you Marilyn’s old dressing room,’ and Parkside House, the house that Marilyn rented, we filmed there. You just felt the echoes of the thing.”

Watch the trailer for My Week With Marilyn.