Credit: Samir Hussein/WireImage

Duchess Kate is the Ace of Cakes!

Prince William's wife and her mom, Carole Middleton, went on a shopping expedition last Saturday, Sept. 3, in Hungerford, England, near the Middleton family home in Bucklebury.

And fashion icon Kate, 29, who was spotted picking up home goods in London earlier this week, didn't have bed linens or skinny jeans on her shopping list this time.

Instead, Kate and her mom picked up supplies at Kitchen Monger -- and Kate's ready to bake!

"She bought a rather nice cast iron kitchen roll holder, but mainly she was buying baking trays in a few different shapes," an observer tells Us Weekly, adding that Kate seemed to be prepping to make "big cakes," perhaps for sister Pippa's 28th birthday on September 6.

England's future Queen stopped by Kitchen Monger just one week before her April 29 wedding to Prince William, 29, and picked up cupcake-making supplies.

"It's lovely that she shops for herself," says the witness, "and so lovely that she still comes back to the shops she grew up near."