Flag Sheet Cake

Trim any rough edges from cakes using a serrated knife. Place four strips of parchment paper around the perimeter of a serving platter. Place first layer, bottom side up, on serving platter. Using an offset spatula, spread cake with 2 1/2 cups frosting. Top with remaining layer, bottom side up. Spread entire cake with 5 1/2 cups frosting. Place remaining frosting in a large pastry bag fitted with a star tip (such as Ateco #35). Remove parchment paper strips. Using the tip of a toothpick, outline the shape of a flag on the cake. Fill the upper left-hand corner with a single layer of blueberries. Place one row of raspberries across upper edge of cake to form first red stripe. Pipe one row of stars just below raspberries to form first white stripe. Repeat process with remaining raspberries and frosting until you have 7 red and 6 white stripes.