To complete the fun, I also made a rainbow fabric chain and a "Happy Birthday" banner to decorate at the party.
I decided to decorate the outside very simply to let the rainbow colors inside really shine. I used plain white frosting and added a ring of rainbow sprinkles on top.
What you need:
- 3 box cake mixes (white)
- 6 mixing bowls
- food coloring
- 9" round cake pans (3)
- cake leveler
- 3 recipes white buttercream frosting (such as Wilton's buttercream)
- rainbow sprinkles, decorating bag and tips
1. Prepare the cake mixes as directed on the box. Divide into six separate bowls. Use the food coloring to dye each bowl a different color. I used concentrated gels to get bright colors.
2. Grease the bottom and sides of the pans. Trace around the bottom of the pans on parchment paper and cut out three circles. Lay one parchment paper circle in the bottom of each pan. (This helps the cake to slide out easier after baking). Pour in one color in the bottom, then carefully layer a 2nd color on top. Try to evenly distribute the 2nd color, or you won't get nice layers.
For my three pans, I used: yellow/orange; red/purple, and blue/green.
You may not need all of the batter that you prepared, so you can use the extra to make rainbow cupcakes!
4. When the cake is completely cool, use a cake leveler to level the top. Then, cut the cake into two layers. Theoretically, it should be one purple and one red layer in the picture, but you can see that I didn't get my layers perfect.
I cut out a parchment paper circle and laid it between the layers, put both layers back in the cake pan, and wrapped the whole pan in plastic wrap. Then I froze the cake for a day. This step is optional, but it really helps when decorating to start with a cold cake. Make sure to remove the parchment paper from the bottoms before assembling.
6. I assembled the cake starting at the bottom, with a layer of frosting between each color:
6. I used plain white frosting to ice the outside. Then I used white icing to pipe a shell border on the bottom. Then I carefully added a ring of rainbow sprinkles on top.
Cutting the cake--yay, success! Enjoy your rainbow birthday cake :)