I made this for a good friend's little girl's 6th birthday. She requested bright pink, and I added the purple base for contrast. Hope she loves it!! The base is a single layer 12" round and the doll's dress is a wonder mold cake on top of an 8" round (to add enough height for Barbie's legs). I wrapped barbie from the waist-down in foil, then inserted her directly into the wondermold and 8" round stacked cakes. The top of her dress and the little flowers are made from fondant... the rest is all buttercream.
This is for a little boy's first birthday party. The bottom tier is 11 inches square, the top tier is 6 inches square. It is frosted in buttercream with fondant dots and hand sculpted fondant animals, including a lion, monkey, hippo, snake, zebra, tiger and giraffe. The lion face cake is the birthday boy's smash cake. It is carved from a 6-inch cake. The mane and nose are fondant, the remainder is buttercream. 
