We took a classic red velvet cake and turned it into red and blue velvet for July 4th! These individual cakes come together by punching out small cake circles and layering them together with a delicious cream cheese frosting.
Preheat the oven to 350˚ F. Make the cakes: Spray two 9-by-13-inch baking pans with cooking spray; line the bottoms with parchment paper and spray the parchment with cooking spray. Combine the cocoa powder and hot water in a small bowl and whisk until smooth; let cool slightly. Whisk the flour, salt and baking soda in a large bowl. Combine the vegetable oil, granulated sugar, buttermilk, eggs, vanilla and vinegar in another large bowl, then add the cocoa mixture and whisk until very smooth. Add the flour mixture and whisk until smooth.
Divide the batter evenly between 2 medium bowls. Whisk 2 teaspoons red food coloring into one bowl until combined. Whisk 2 teaspoons blue food coloring into the other bowl until combined; add more blue food coloring, 1/4 teaspoon at a time, to make the batter royal blue.
Evenly spread the red batter in one pan and the blue batter in the other. Bake until the cakes spring back when gently pressed and a toothpick inserted into the centers comes out clean, about 15 minutes. Transfer to racks and let the cakes cool 10 minutes in the pans; carefully turn out the cakes onto the racks to cool completely. Remove the parchment.
Transfer one cake to a cutting board. Starting at the very edge of the cake, use a 3-inch round cutter to cut out 12 rounds. (Do not leave any space between the rounds when cutting.) Repeat to cut out 12 rounds from the other cake.
Make the frosting: Beat the cream cheese and butter in a large bowl with a mixer on medium-high speed until well combined. Add half of the confectioners' sugar and the salt and beat on low speed to combine. Beat in the remaining confectioners' sugar, then increase the speed to medium high and beat until light and fluffy, about 3 minutes. Add the vanilla and beat until combined, about 30 seconds.
Assemble the cakes: Spread about 2 heaping tablespoons frosting on the top of each cake round. Stack them in tiers of three, alternating red and blue layers (some cakes will have 2 blue layers and some will have 2 red). Top with sprinkles.