I made this cake for my 6 year old's art/rainbow birthday party last week. It really was so much fun to make! I got the idea over at Martha's.:) I made it easier on myself and used 2 plain white cake mixes to start the cake because I wanted the cake layers a little thicker than that version. I did use the Lemony Swiss Meringue Buttercream recipe. This buttercream did a great job holding up between all the layers! I would recommend it when making this particular cake.
1. I took two white cake mixes and mixed them up in a large bowl according to the directions on the box. Then I divided the batter into 6 different bowls. Each bowl ended up with about 1 and 3/4 cups of batter each. Then I mixed some food coloring into each bowl to get my rainbow colors. Only use the gel food colors! You really only need a very small amount in each one.
2. When each color is mixed, place batter into 6 separate round 9 inch pans. I only had three, so I baked 3 first and then when they had cooled, I transfered the cakes to a cookie sheet. I washed the pans and baked the other 3 cakes. Be sure to grease your pans well so that the cakes come out without sticking. I baked the cakes in a 350 degree oven for about 12 minutes.
3. After all the cake layers have cooled, place your bottom layer (purple) onto your cake plate. Add a thin layer of frosting. Place your blue cake layer on top of the frosting. Continue in this manner until you have added all your cake layers.
4. Crumb coat: after you have your cake layers placed together, take your frosting and lightly frost the entire cake (sometimes it helps even more to freeze the cake for an hour before crumb coating). This layer will have a lot of crumbs in it, but don't worry, they will not show. Place the cake back in the freezer or fridge for an hour.
5. Take your cake out and frost the entire cake.
6. I topped mine with a skittle rainbow and marshmallow clouds.
TIP: Right after you have frosted the entire cake, take your flat spatula and dip it into a tall cup of hot water. Then with it clean of frosting, run it over the frosting layer to give it a smooth finish. I continue washing the spatula in the hot water over and over until I like the results.
After the stacking and before the crumb coat: