I bought the mold with doll included from a party store for about $30, all the supplies I used I bought there but mixing it up is the fun part. Here is how I did this Princess Cake:
The cake mix I used was a pound cake because I used A LOT of fondant and pound cake supports heavy fondant really well. Please note that I had to bake the pound cake longer than usual due to the amount needed to fill the mold.
After the cake is done and cooled I started decorating. Before adding the fondant I coated the cake with a layer of strawberry icing to give the cake a yummy flavor. Roll out your fondant to a thickness your happy with (on wax paper). Slide your hands under the rolled fondant and gently place on the cake. The fondant should lie in a "ruffled" affect that you see on this cake.
To make it more uniformed ruffles just overlap and press gently so that it will stick.
Her top was made with leftover fondant molded ( and thinned out slightly) over her bust. I made the sprinkles sticks my rubbing a small amount of sugar water over the area I wanted to be pink. Her belt is a stand alone piece using the same method.
Her present is fondant but you can use gum paste or marzipan with a toothpick to hold it into place. Use fondant gel to make the flowers. Or you can cut them out from fondant colored with strawberry icing. The trim on her dress is just a jar of candy that I bought at the party store held in place by strawberry icing piped through a pastry bag.
You can do whatever you like with her hair but I HIGHLY suggest that you fix her hair PRIOR to placing her in the cake.