Rainbow cakes are all the rage right now. They are bright and colorful and add a touch of whimsy to any party.
The only downside to these cakes is the amount of artificial food coloring used to tint the cake batter. Good news: You can use natural colorings made from things you can find in your own refrigerator! Things like carrots, spinach, beets, blueberries, blackberries, and egg yolks. The juice from these fruits and vegetables can be used to make pretty, colored batter that bakes into soft pastel colored cakes and (surprisingly) imparts very little flavor! I was very hesitant to taste the spinach and beet layers, but was happy to find that they just tasted like cake – not like the vegetables used to color them!
I've seen rainbow cakes made from scratch that use natural colorings, but I wanted to take a shortcut and use Betty Crocker cake mixes and frosting. I decided it would be easiest to start with one yellow cake mix to make my yellow, orange and green layers, and one white mix for the fuchsia, purple and blue layers.
You can buy the fruit or vegetable juices from health food stores or just make your own. If you have a juicer, this is an easy task. If not, you can puree the fruits or vegetables in a blender, or use a stick blender (as I did). Then pour the chunky puree into a fine mesh strainer, and press on the solids with a rubber spatula or spoon, expelling the juice into a bowl set under the strainer. You'll need 2-3 tablespoons of each juice to add to the cake batter. The amount of fruits or vegetables you'll need will depend on how you juice them. I suggest having about 2/3 to 1 cup of carrots, blueberries, blackberries and spinach on hand. For the beets, you can puree them, or just use the red juice from a can of beets.
Make the yellow cake batter and divide it equally into three bowls.
In one bowl, make the yellow layer by adding a egg yolk. In another, add carrot juice to make orange, and finally, add spinach juice to make the green batter.
Make the white cake batter, then divide it into three bowls. Add two tablespoons of beet juice to one bowl to create fuchsia batter. Then add three tablespoons of blueberry juice to another bowl to make blue. In the final bowl, add two tablespoons blackberry juice plus one teaspoon beet juice.
Pour batter into baking pans. I used 8-inch round springform pans. I lined the bottom of each with non-stick tin foil, which made removal very easy.
Bake the cakes, cool, then trim off rounded tops (if needed).
Place purple cake on a cake round or serving plate. Spread frosting over cake layer, and then repeat with blue, green, yellow, orange and fuchsia cake layers.
Spread a light coating of frosting on the top and side of the cake to seal in crumbs, and then frost with remaining frosting.
All that's left is to cut a slice and enjoy your beautiful rainbow cake!