Preheat oven to 350°F. Grease and flour two 8-inch or two 9-inch round baking pans; set aside. Prepare cake mix according to package directions. Divide batter between pans. Bake according to package directions. Cool in pans on wire racks for 10 minutes. Remove cake layers from pans. Cool completely.
Spread 2/3 cup of the frosting on one of the layers. Top with remaining cake layer. Frost top and side of cake layers with dessert topping. If desired, in a small bowl stir together remaining 1/3 cup frosting and milk. Drizzle over frosted cake. Decorate top of cake with whole or sliced berries.