"Wearing a pregnancy suit was so much fun," the actress, 33, tells PEOPLE. "I loved the feeling of pretending to be pregnant and having little arms and legs and this big belly."
But it wasn't just the suit that got her thinking about motherhood. "I've been wanting to have a baby since I was 2 years old – I'm destined to be a mother," says Silverstone, who will celebrate her fifth wedding anniversary with musician-husband Christopher Jarecki on June 11. "I can't wait to be pregnant."
She'll hold off for now, though, since she's busy filming the upcoming comedy Butter with Jennifer Garner in Shreveport, La. "It's an interesting place, but you're working so much, so it's not like you're on vacation," she says.
Silverstone, whose vegan cookbook The Kind Life recently topped The New York Times bestseller list, will soon put her own personal eating habits aside to play a vampire in the upcoming comedy Vamps, directed by her Clueless writer-director Amy Heckerling.
"Amy came to see me in the play because we're friendly," says Silverstone, who starred as Cher in the iconic 1995 comedy. "But afterwards, we hung out and she introduced me to her producing partner … a few weeks later they called me and said I got the movie."
In addition to looking forward to playing a vampire ("It'll be so much fun," she declares), Silverstone is psyched to reunite with her former director.
"I was a baby when we met," she says. "It's crazy how long ago that was. Now it'll be great to be a grownup and work with her."
And yes, Silverstone says she still gets recognized "every single day" for Clueless. Not that she minds. "It's never been a bother," she says. "I have nothing but joy when somebody says they love that movie."