My daughter wanted a Barbie cake for her fourth birthday. I wanted to do one that had the entire doll inside, as I did one for my older daughter when she turned four, and she was hysterically upset when she pulled the doll out and found she had no legs, so I needed to make the cake tall enough to hold the Barbie complete with legs.
I cooked two packet cakes, one in a small stainless steel mixing bowl, and one in a 20cm cake tin. I froze them separately, then took them out and gouged out a hole for the doll while they were still frozen. Then I made up some butter cream icing, glued the round cake to the plate with some of that, then glued the two cakes together, wrapped Barbie's bottom half in plastic wrap and inserted her into the cake.
Then I shaved some of the edge off the bottom cake to make a better dress shape and used these offcuts to taper the top of the cake round Barbie's hips. I just glued bits on with the butter cream icing higgledy piggledy, not worrying about being too neat, as I figured all of this construction would be covered by the top layer of icing.
To do the dress, I bought some royal icing. I started with the white panel at the front by rolling out a small piece in a sort of wedge shape. I glued it on with icing sugar and water made into a paste, painted on with a pastry brush. Then I did the pink part of the skirt by kneading some icing, then I dripped some red food colouring on and kneaded it in till it was evenly dispersed through the icing. I did the pink part of the dress in two parts to make it easier to handle. I did one side, then the other, with a join in the middle at the back. I cut the dress to length once it was on the cake. Then I made the ribbons to hang down the back by rolling out two pieces into long sausages then rolling them flat with the rolling pin. I glued them on like the other bits.
To make the bow I made a kind of leaf shape and rolled it flat. I wrapped them round wooden spoon handles to keep their shape. Then I just glued them in place and put a wee piece in the middle to cover the join. For the bodice I just made a long rectangle and stuck it on, then I shaped it with a little sharp knife while it was on. I made a little narrow white "belt" to cover the join and stuck pink edible pearls on it with a few down the front. Then I made tiny white balls of icing, flattened them with my fingers, stuck them on and pressed a pink pearl into the middle of each one all over the dress.
I got lots of ideas from this site. There are some gorgeous cakes here!