Rainbow Cake

I received a request earlier this week to help a friend bake a cake for her girlfriend's birthday.

She wanted a Rainbow Cake.

It was a simple vanilla cake recipe, and we decided on homemade vanilla pudding as the filler, and chocolate buttercream frosting to hide the colorful interior (surprise!!!).

Cake batter dyed and ready to go!

Cake (some changes to this cupcake recipe): 
Ingredients

1 3/4 cups (175 grams) cake flour, not self-rising (Or use 1.2 c. AP flour and 1/4 cup cornstarch)
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1 cup (225 grams) granulated sugar
1/4 cup (57 grams) unsalted butter, room temperature
2 large eggs, room temperature
1/3 cup (75 grams) vanilla greek yogurt
1/4 cup canola oil or vegetable oil (60 ml)
1 tablespoon pure (not imitation) vanilla extract
2/3 cup (160 ml) milk
Instructions
1. Preheat oven to 350 F (175 C). Line a jellyroll pan with buttered parchment paper.
2. In a small bowl, combine sugar and butter and flour until well blended. Add eggs, vanilla greek yogurt, oil, and vanilla and mix well.
3. In another bowl, mix together cake flour, baking powder, baking soda, and salt.
4. Add 1/3 flour mixture to sugar mixture and mix until JUST combined, then 1/2 of the milk and mix, then 1/3 of the flour, then the rest of the milk, and then the rest of the flour.
5. Divide the batter into six equal portions, or however many colors you want. Dye each.
6. Spoon batter out onto the pan in rows.
7. Bake for 9-11 minutes or until the cake springs back when you touch it. Let it cool.

Baked rows in the pan. Cut this into 4, and stacked opposite sides.

While you're waiting, make the Vanilla Pudding Filling and the Chocolate Buttercream Frosting (add 1/4 cup cocoa powder, or some melted chocolate, and some more milk until desired consistency is reached). Divide the cake as you wish, fill, stack, frost. Donezo, and you have a happy birthday girl!

Finished cake! Alternated colors for full rainbow effect.