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American Flag Cake

American flag cake is a white sheet cake covered in smooth buttercream and topped with a crisp blueberry canton plus neatly rowed strawberry red stripes and white stripes. It’s built from boxed white cake mix for easy assembly and a clean, vivid Independence Day look.
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Prep Time 45 minutes
Cook Time 35 minutes
cooling 1 hour
Total Time 2 hours 20 minutes
Servings: 20 servings
Course: Dessert
Cuisine: American
Calories: 420
Ingredients Equipment Method Notes

Ingredients
  

white cake mix
  • 2 boxes white cake mix Use the ingredients listed on the box (eggs, water, and oil/butter), in the amounts for two 9x13 cakes or two pans as directed.
buttercream frosting
  • 2 cup unsalted butter Soften before beating.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 5 tbsp heavy cream Use 4–6 tbsp total to reach spreadable consistency.
fruit decoration
  • 2 cup fresh blueberries Keep cold and dry for clean layering.
  • 2 lb fresh strawberries Hulled and sliced lengthwise; aim for uniform rows.
  • 1 banana slices Optional for white stripes; otherwise use extra white frosting.

Equipment

  • 1 sheet pan

Method
 

Bake and cool the cake
  1. Bake both cake mixes in a large 12x18 sheet pan or two 9x13 pans joined together according to package directions, then cool completely.
  2. Let the cakes cool to room temperature before frosting so the buttercream stays thick and smooth instead of melting.
Make the white buttercream
  1. Beat the softened unsalted butter until fluffy, then gradually add powdered sugar, vanilla extract, and heavy cream.
  2. Continue beating until smooth and spreadable, adding 1 tbsp more heavy cream if the frosting is too thick.
Frost and decorate like a flag
  1. Frost the entire top of the cooled sheet cake with a thick, even layer of white buttercream.
  2. In the upper left corner, arrange fresh blueberries into a dense rectangle to form the blueberry canton.
  3. Create red stripes by laying sliced strawberries flat across the length of the cake in uniform rows.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows, or place thin banana slices for the white stripe look.
Chill, slice, and serve
  1. Refrigerate until ready to serve, then slice into squares.
  2. For clean cuts, dip the knife in hot water, wipe dry, and repeat between slices.

Notes

Pro tip: for the cleanest flag pattern, use uniformly sized strawberry slices and keep fruit dry before decorating. Refrigerate covered up to 3 days; freeze unfrosted cake layers only (not decorated fruit). For a dietary swap, use lactose-free butter and lactose-free cream in the frosting to reduce dairy sensitivity while keeping the texture similar.