This was the princess barbie cake I made for my granddaughters 3rd birthday last year.
The ones in the shops are really small and she wanted a bigger one so I did my best. It didn't turn out too badly. I bought a barbie doll and then stripped the clothes of and wrapped the body in cling film to protect it. I used a pudding basin for the skirt of the cake, this one was chocolate, as requested by Miss Lily lol.
When the cake was ready I turned it upside down and then used plain white fondant icing to make the skirt. I let the fondant crease at the bottom to make the folds of the skirt. I then used an apple corer to take out the centre of the cake and put the clingfilm wrapped doll inside. I wrapped the upper body of the doll in icing and then tied a ribbon around the waist.