Preheat oven to 350ºF. Grease and line two 8-inch round cake pans. [See Note 4]
In a medium bowl, whisk together 1 box of cake mix, 1-¼ cups water, 1/3 cup vegetable oil, and 3 egg whites. For a pure white cake batter to be tinted, do not use the egg yolks.
Mix vigorously by hand or on the medium speed of an electric mixer for 2 minutes.
For Rainbow cake: Divide the batter evenly between 6 bowls (about ½ cups each bowl). Then color each of the batters using the following recipe:
Red – 15 drops of red
Orange – 5 drops of yellow and 2 drops of red
Yellow – 8 drops of yellow
Green – 9 drops yellow plus 2 drops of blue ( or 11 drops of green)
Blue – 14 drops of blue
Purple – 7 drops red plus 2 drops of blue
Next, layer the cake batter evenly into the prepared cake pans one color at a time starting with red. Pour ¼ cup of batter into the center of the pan and allow it to gradually spread into a circle on its own. Do not touch the batter once it is in the pan.
Next, pour ¼ cup of batter into the center of the pan on top of the red batter.
Continue with the rest of the batter colors: yellow, green, blue, and purple. Remembering to allow each color to spread evenly on its own. Level the pan by gently shaking the pan.
Bake for 30 to 35 minutes or until a cake tester inserted in the center comes out clean. Allow to cool for 5 minutes before inverting cake onto a wire rack. Cool completely.
Repeat steps 1-8 with the second cake mix. [See Note 5]
Once cakes have cooled completely, level them with a cake leveler or serrated knife. Having level cakes free of the rounded “dome” tops is essential for cake stability and construction.
Prepare the cake frosting by first creaming the butter and shortening together in a large mixing bowl. Then in stages, add in the powdered sugar, and vanilla. Add the milk 1 tablespoon at a time until you get a stiff but spreadable frosting. A frosting too thin will not be able to pipe flowers in the second batch.
Stack first of the cakes tiers on a 9-inch cake board or cake stand. Fill a large pastry bag with white frosting. Pipe rings around the inside edge of the cake layer and then fill in the circle with more frosting. Then smooth the frosting out evenly with a knife. Carefully add the next layer so that it is center. Once the second layer is center, press the cake firmly down with the palms of your hands being careful not to break the layer. Then again pipe in the frosting and spread it evenly with a knife. Repeat this process two more times until all 4-cakes are frosted and stacked.
Next, put a really thin coating of white frosting over the entire cake. It doesn’t have to look neat or finished. This is the “crumb layer”. It locks the stray crumbs into frosting so they do not end out on the outside of the finished cake. [See Note 6]
Once the crumb layer is on, refrigerate for 25 minutes, if possible. I do this to lock down the crumb layer before I start with the finished frosting layer.
With a piping bag filled with white frosting, pipe circles of frosting over the outside of the cake and over the top. This is easiest with a turntable but can be done by gently moving the cake stand.
Running the knife under hot water and wiping with a paper towel between uses helps make the frosting really smooth. Remove excess frosting back into the mixing bowl.
For an 8-inch, 4-layer cake, you will use all or nearly all the first batch of pure white frosting.
Piping the Mane:
Prepare the second batch of frosting the same at the cake frosting following step 11.
Divide the frosting evenly between 6 bowls (about 2/3 cups each).
Prepare the frosting colors as directed in sub-step 4.
With a toothpick I made a small arrow in the top of my cake to mark the front center if the cake (it later was piped over with swirls and flowers. Using that mark I created, I “eye-balled” the placement of the flowers, how they would fall over the back side of the cake and flow along the side along to end at the front center of the bottom of the cake.
Starting with red, I piped about 8 – 10 “rosette” swirls starting a little off center and then in a few inch increments along the imaginary line I had to how the main would fall. I repeated this cleaning the tip between colors and then, with the same 1M tip, pipe small star shaped flowers as needed to fill in any gaps. Repeat this with the remaining colors.
Pipe eyes onto the front center of the cake. Place horn on the top center of the cake and the ears on either side of the horn.
Enjoy the rewards of all your hard work - the kids will LOVE it!
White cake mix yields the best results as compared to a standard yellow cake mix.
Use egg whites only (no yolks) for best results. Do not use egg beaters or other boxed egg whites - they are not recommended for baking.
Clear baking vanilla is best to keep the cake mix as white as possible, but regular vanilla may be substituted.
I used 1 cake pan four (4) separate times, if you have 2 or 4 8-inch pans you can always bake all 4 layers at once. I oiled the pan with non-stick cooking spray and then lined it with a round parchment paper disc. I then also sprayed the parchment with non-stick cooking spray to prevent the cakes from sticking to the pan.
I prepared each cake mix separately. Some cake mixes do not do well when doubled.
The crumb layer is a very thin layer, you can usually still see through it. It's only purpose is to lock in any cake crumbs so they do not get onto the outside layer of the cake.