I don't make cakes that I have to carve as a rule. But sometimes rules just have to be broken! I had the idea of this cake in mind for my sister's birthday, and I tried to convince myself to make the dress and mannequin as a topper instead, but couldn't let myself get away with the cop-out. So, after a restless night filled with cake-dreams, I took the plunge. There are no work-in-progress shots, because I didn't actually think I'd pull it off! The mannequin is black fondant mixed with…