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Minnie Driver and about 40 guests gathered Saturday at a friend's home in Malibu for a baby shower.

The house was decorated with pink and white peonies, and it was a casual affair, with guests sipping basil lemonade and eating finger sandwiches and berry cake from Sweet Lady Jane.

"Minnie loves the cake," says a pal.

Driver opened Gymboree Brand New gifts, while guests hand-painted onesies for the baby and signed personal notes in a book to be given to the mom-to-be.

"It was a beautiful day," a guest tells PEOPLE.

The British-born Driver, 38, has decided not to find out the sex of the baby. She has said little about the father, except that's he's English, "sort of in the same business," and that they have no plans to marry.