My daughter has a wide range of interest and loves, so when she said she wanted a Barbie cake for her 6th birthday (while celebrating her brother's 8th birthday), I figured she would change her mind several times before the big day as she does with so many other things. Imagine my surprise when I asked her a couple weeks before the big day what kind of cake she wanted, and she reminded me she already told me 6 months ago at her brother's birthday.
Standing the Barbie up next to several of my baking dishes, I settled on 2 7-inch rounds, 1 8-inch square (that I figured I would just freeze and use for later), and one 1-qt Pyrex bowl. The 7-inch rounds took a surprisingly long time to bake (I did fill them at least half full, which is maybe fuller than you normally would), so I turned the heat from 350 down to 325 so they wouldn't burn/dry out. They stayed nice and moist. 2 cakes were yellow, 2 were devils food.
After I un-panned and cooled all the layers, I could not believe how tall this cake needed to be to accommodate the doll's legs! This was her favorite Barbie so I couldn't cut the legs off. I wound up using the 2 rounds, the dome, and some sliced up square as filler to make up for the height and fill out the bottom so it didn't look like a tube and then I still had to figure out more height without making it too wide/too sharp an angle at her waist. Fortunately, my husband has been on a donut kick so I grabbed one of those, broke it in half and put it around her waist like an inner tube.
I put her on an inverted dinner plate because we were going to try to bring her to the ballpark where we were having her birthday celebration, and were trying to fit her sideways into a cooler (that wound up not working out, we left her at home and all came back to the house for cake).
I used a long knife to make a triangle in the stacked cakes and wiggled it around a bit to make room for the doll; I double wrapped her in cling wrap, pushed and wiggled her in and crossed my fingers that the cake didn't crack. I crumb coated it with a standard butter cream (1 c butter, 1 c coconut oil or Crisco; 7-8 cups *sifted* powdered sugar (yes, do take the extra step and sift it!), 2-4 Tbsp milk or cream - whip fats to fluffy, add sugar a little at a time, add milk to desired consistency, then let it rip for 5-7 minutes to achieve maximum fluff.
I tinted and frosted the skirt part and then ran out, so I stuck it in the freezer until the next morning (it was 2am by this time, I work nights and did this part when I finished work). I made another full batch of tinted butter cream for the piping in the morning. Daughter asked for stripes, but I broke them up a little with the ruffles in the middle and the hemline. I was quite pleased with how the ruffled top came out. I was afraid it was going to be too thick and I'd lose her torso shaping/waistline. I used a star tip for the hemline, ruffles, and bodice, and a flat tip for the swags. I piped a rosette on the edge of the plate to put in the candle, as I had seen here a couple times.
This site was an IMMEASURABLE help to me in making this cake! I am so glad I spent an hour or so reading through and looking at pictures before I took this on!