This Barbie birthday cake sells for up to $60 (or more!) in stores, but you can make it with time and patience. The dress is a cake baked in a Pyrex bowl. You can use a Barbie you have on hand or buy the torso at a baking supply store.
I cut a hole in the cake for Barbie. I put a crumb coat on it and let it set in the freezer for about 30 minutes. Make sure you have a nice, stiff butter cream frosting or it will run (I made the cake in August). I then frosted the dress on, making the swirls with a spatula. I piped the bodice on with a small star tip and added some pink detail to the dress. You can also use sprinkles, pearl dust for details.
My daughter loved the final result, and I loved the challenge!