I used a simple chocolate cake recipe for the base of the cake.
For the fondant detail please see below.
I used 4 layers for the cake(double the recipe shown in above link) , although I felt a 5th layer would have helped given the size of the cake, but then the fifth layer would anyways be trimmed to bring the shape of the skirt, so I used the tops of the existing layers to give the skirt shape and the extra little height.
1.Apply little butter cream on the cake board.Place the first layer on top.Apply butter cream on the layer and place another layer on top,repeat until all layers have been placed.Make sure they are all standing straight and are not slant.I did not flatten the topmost layer to give the dome shape of the skirt.
2.Now , remove the skirt of the Elsa barbie doll.Wrap her legs in surround wrap. Make a hole in the center of the cake and scoop out a hole from all the layers so you can push the doll in without hurting your cake. Keeping all the layers in place gently push the doll inside so the legs tough the bottom.IF you are making a bigger/taller cake, it need not touch the bottom.If using a 5 th layer trip the top layer to give the shape of the skirt.I just used an extra layer of the dome of another layer to give that effect.If you top layer cracks thats fine, because the fondant is going to cover all of it anyway.Apply buttercream all around covering the entire cake.
3.Now measure the height of the cake from the bottom to the hips area,roll out your fondant so the radius is atleast 1 inch more than the height of the doll and diameter is atleast a double +2.For example if the height of the doll is 8 inches, roll the fondant to 8*2+2=18 inches diameter.Do not roll out too thin or it will tear due to the height of the cake.If your fondant is drying out in this process, mix it with vegetable shortening.Then place a hole in the enter as the diameter of barbies hips and a slit so you can wrap the skirt around.Do measure these carefully because you have one chance to put the fondant on.
4.Wrap the fondant around the doll, and place a circular tube of fondant around the hips to cover the crease.I also did an extra layer just to give the dress some body.Gently arrange the pleat of the dress to give it a free falling look.
5.Roll out another piece of lighter blue or white fondant with height that will reach the shoulders of the doll from the cake board and width that will come across both sides of the doll.
6.Drape the fondant around the dress like a cape, you can pipe stars on to the fondants before you place them on, or you can use sugar charms and stick them on the fondant with some butter cream or you can make some shapes/prints using cookie/fondant cutters on the fondant.I also blew some silver dust onto the cape and skirt to give it a starry glittery effect.