Rainbow Marble Cake (Print Version)

# Ingredients:

01 - 3 cups all-purpose flour.
02 - 3 cups granulated sugar.
03 - 2 1/2 tsp baking powder.
04 - 1 tsp salt.
05 - 1 cup unsalted butter, room temperature (2 sticks).
06 - 2 tsp vanilla extract.
07 - 1 cup egg whites (about 7 egg whites).
08 - 1 1/2 cups buttermilk, room temperature.
09 - 1/8 cup vegetable oil.
10 - Gel food coloring in purple, blue, green, yellow, orange, red.
11 - 3 cups unsalted butter, room temperature (for frosting).
12 - 11 cups powdered sugar (for frosting).
13 - 1 tsp salt (for frosting).
14 - 1/3 cup heavy cream (or whipping cream for frosting).
15 - 1 1/2 Tbsp vanilla extract (for frosting).
16 - Gel food coloring in purple, blue, green, yellow, orange, red (for frosting).

# Instructions:

01 - Vanilla Cake Layers: Preheat oven to 350°F (177°C). Line three 8-inch round cake pans with parchment paper and grease the sides.
02 - In a stand mixer with a paddle attachment, mix flour, sugar, baking powder, and salt until combined. Gradually add the butter until the mixture becomes crumbly.
03 - Mix in egg whites on low until just incorporated, then gradually add buttermilk. Add vanilla extract and oil, mixing on low. Scrape the sides of the bowl and beat on medium for 30 seconds.
04 - Divide the batter evenly among six bowls and color each with a different gel food coloring. Spoon the colored batter into the pans, creating a marble effect with a knife. Use blue and purple in one pan, and vary the colors in the others as desired.
05 - Bake for 34-37 minutes. Cool for 10 minutes in the pans, then transfer to the freezer for 45 minutes to firm up.
06 - Vanilla Buttercream Frosting: In a mixer, beat 3 cups of butter for about 30 seconds on medium speed. Gradually add powdered sugar, alternating with cream, and beat until smooth.
07 - Mix in vanilla extract and salt. Adjust consistency with more cream or powdered sugar if needed. Keep the frosting white for assembling the cake, reserving some for coloring later.
08 - On a greaseproof cake board, stack the cake layers, spreading buttercream between each layer. Apply a crumb coat of frosting over the cake and chill until firm. Add a final layer of frosting and smooth with a bench scraper.
09 - Divide and color the remaining buttercream, then use French piping tips to decorate the cake with rainbow stripes around the sides.

# Notes:

01 - Spoon and level the flour for accurate measurements.
02 - Use room temperature ingredients to ensure smooth mixing.
03 - Opt for gel food coloring to maintain the batter and frosting consistency while achieving vibrant colors.
04 - Chill the cake layers in the freezer for easier handling when assembling the cake.

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