Red, White, and Blue Flag Cake 2:50 Prep Time: 1 hr Total Time: 1 hr Servings: 24 For a patriotic dessert designed to feed a crowd, look no further than this showstopping flag cake. It all starts with two layers of Martha’s basic white sheet cake that's tender, moist, and full of vanilla flavor. Sandwiched between and spread on top is a rich and tangy cream cheese frosting. Fresh blueberries and raspberries form the stars and stripes, along with piped rows of more frosting.