01 -
Preheat oven to 350°F and grease a 9" x 13" baking dish.
02 -
Combine cake mix, water, egg whites, vegetable oil, sour cream, and vanilla extract in a large mixing bowl or stand mixer. Mix on low speed until ingredients are combined, then beat on medium speed for 2 minutes, scraping the sides of the bowl as needed.
03 -
Pour 2 cups of cake batter into the prepared baking dish. Divide the remaining batter equally into three bowls. Add a different food coloring to each bowl and mix until colors are consistent.
04 -
Drop dollops of each colored batter randomly over the white batter in the baking dish. Use a butter knife to swirl the colored batters together without overmixing.
05 -
Bake for 30-35 minutes or until a toothpick inserted in the middle comes out clean. Let the cake cool completely.
06 -
Beat softened butter in a mixing bowl until light and fluffy. Mix in salt.
07 -
Gradually add powdered sugar while mixing on low speed until fully incorporated, scraping the bowl as needed.
08 -
Add vanilla extract and 2 tablespoons of heavy cream. Mix for one minute. If frosting is too thick, add more cream until desired consistency is achieved. Add food coloring if desired.
09 -
Frost the cooled cake. Garnish with pastel sprinkles or Easter-themed candies.