Not only was the leadership top-notch - Steven Spielberg and Oprah Winfrey are producers and Lasse Hallstrom directs - the project allowed Mirren to make good on a lifelong dream.
"I've always secretly wanted to be a French actress and never actually managed it," she said.
Adding to the charmed project was its picturesque setting in the south of France ("You'd think you're in an ad for France, but it's all real," Mirren said) and nightly home-made meals by co-star Om Puri, who plays the patriarch of the Indian family.
"It was one of those absolutely blessed experiences," Mirren said - the kind that makes her question a film's quality. But she quashed that fear: "We had Lasse, and Lasse was our secret weapon."
The director said Mirren - in character and out - added to the magic on set. "She's so smart and skilled," Hallstrom said. "She knows every aspect of film-making."
Except how to feel comfortable between projects. Time off makes her anxious. She fears breaking her concentration and losing the momentum of the character she's meant to play.
Mirren said that when she sees movies or theatre, she feels "blown away" by other actors' work and fearful of her own ability to execute.
"And then maybe [I've] got a project coming up, and then I get really nervous because I think, 'I can't do that'," she said. "Then, of course, you start and you realise, 'Oh yes, I can. This is what I do. This is my job.'"
Who: Helen Mirren
What: The Hundred-Foot Journey, directed by Lasse Hallstrom
When: Opens at cinemas on Thursday
- AP