Preheat oven to 350°F. Grease and flour a 15x10x1-inch baking pan; set aside.
Prepare cake mix according to package directions. Spread batter evenly in prepared pan. Bake for 15 minutes or until top springs back when lightly touched. Cool cake in pan on a wire rack. Once cool, freeze for 20 minutes until slightly firm.
Use a 4-inch round cutter to cut 6 circles from the cake. Place 3 of the rounds, top sides down, on plates. Use an offset spatula to spread some of the frosting over top of each round on plate. Top each with another cake round, top side down. If desired, add a crumb coat to the top and sides of each. Chill for 10 minutes, then frost top and sides.
Tint the remaining frosting desired color. Fill a decorating bag fitted with a star tip with frosting. Pipe on each cake. If desired, decorate with sprinkles.