- Preheat your oven to 350 degrees.
- Weigh your mixing bowl (you’re going to need to know this later) – If you don’t have a scale, skip this step.
- Combine your vegetable oil, eggs and pudding. Once they’re all mixed together add in your cake mix. Your batter is going to be VERY thick so if you’re using a hand mixer, you might want to finish it off by hand.
- Weigh your batter in the mixing bowl. Okay, here’s where math comes in. Subtract the weight of the mixing bowl then divide that number (batter weight) by 6. Got it? Write that number down.
- Take your small mixing bowl and weigh that without anything in it. Got it? There should be a little “barre/on” button on your scale. Press it to zero out the weight of the bowl. Now, put in the amount of batter by weight that you got from step 4.
- Okay, now that math is over, you’re going to go ahead and mix your colors. Work backwards starting with PURPLE, BLUE, and GREEN.
- Spray your pans down with non-stick baking spray, pour/spread your mix and stick it in the oven for about 15-20 minutes or until a toothpick stuck in the center comes out clean.
- Once your first round of cakes are done, remove them from the pans and place them on your cooling racks.
- Repeat steps 6-8 but with YELLOW, ORANGE, and RED food coloring.
- Once your cakes are cooled, level each by using your cake leveler or serrated knife. You want each top to be flat. A cake leveler is going to give you nice even layers, but it really just depends on what you have in your kitchen. – Make it work 😉
- Finish each layer off by drizzling simple syrup over the cut tops of each layer
- Cream butter, vanilla and vegetable shortening together.
- Add powdered sugar SLOWLY until its all incorporated.
- When you get about half way through with the powdered sugar add your cream.
Frosting your Rainbow Layer Cake!
Its time to build your cake! Using an offset spatula (or the back of a spoon), spread some frosting on the base where your cake is going to sit. Place the PURPLE layer top up and add a thin layer of frosting. Lay your next layer, BLUE, TOP down. Add a thin layer of frosting. Repeat this step until all 6 layers are stacked.
Give it a quick crumb coat… a super thin layer of frosting. Just enough that pieces of cake don’t come off when you’re doing the actual frosting.
Let that sit for about an hour, then start frosting your cake. Sides first to get an even coating, then top, then sides again.
If you want a smooth finish, dip your spatula in water and use it on your last pass over the cake.
Decorate with skittles and serve the surprise!