This sample recipe is a large 8 inch (200 millimeter) round and 8 inch (200 millimeter) high cake.
Below is the step by step method of achieving the rainbow cake presentation
- 2 batches vanilla cake
- 2-3 batches of vanilla buttercream
- Gel Paste: red, orange, yellow, green, blue, and purple
- Six 12 inch piping bags
- large round tip (Ateco 809 or Wilton 1A or equivalent)
Preheat your oven to 350˚F/180˚C. Grease and prepare six 8 inch (20 centimeter) cake pans.
Prepare the vanilla cake batter. Divide the batter into 6 bowls, and color each one a separate color using ¼- ½ teaspoon (1-3 milliliters) of gel paste for each color.
Bake each colored cake in the oven for 15-20 minutes and allow to cool completely before leveling.
Prepare the buttercream. Leave some of it white for the layers between the cakes, approximately 2-3 cups (240 milliliters- 720 milliliters) and divide the remaining buttercream into 6 bowls, and color each separately.
The order of colors from bottom to top goes purple, blue, green, yellow, orange, red. Starting with the base of the cake, place the purple cake layer onto a plate or cake board and use a swipe of buttercream to “glue” the cake to the base. Add white buttercream on top of the cake layer using a metal spatula and smooth it out evenly.
On top of the buttercream layer, place the blue cake layer, top with white buttercream and smooth. Repeat, alternating between cake layers and buttercream until the final red layer is at the top. Once you reach the top of the cake, cover the entire cake in white buttercream. Ensure that the cake is straight up and down (not leaning), and place into freezer to solidify the layers of buttercream. This will make it easier to decorate without causing the cake to lean.
Petal technique: Place purple buttercream in a piping bag fitted with a large round tip, such as Ateco 806, or Wilton 1A. To make the petal shape, place the tip about an ⅛ inch (½ centimeter) away from the side of the cake, squeeze the piping bag, allow the buttercream to “grow” into a mound, and then pull the bag away from the mound, along the side of the cake, slowly stop squeezing the further away from the mound you get. Line the tip up again where you left off, and repeat the process. I started at the base of the cake with the purple buttercream, went around the cake entirely, and then moved up to blue, then green, yellow, orange, and finally red. Repeat as many times as necessary to cover the entire cake. The same technique is used to cover the top as well.
Slice and serve immediately. The cake can be kept in a sealed container in the fridge for up to 3 days.