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American Flag Cake

American flag cake with a full sheet cake frosted in white and decorated with a blueberry canton, strawberry red stripes, and piped white frosting or banana slices. This patriotic sheet cake is made with two white cake mixes and a smooth buttercream that spreads thick for clean, vivid rows.
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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 base
  • 2 box white cake mix Use two boxes of white cake mix plus the ingredients listed on the box (typically eggs, water, and oil).
  • 2 eggs Use the amount required by the cake mix box.
  • 1 water Use the amount required by the cake mix box.
  • 1 vegetable oil Use the amount required by the cake mix box.
Buttercream frosting
  • 2 cup unsalted butter Softened.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 0.5 cup heavy cream Start with 4 tbsp; add up to 6 tbsp for spreadable consistency.
Flag decorations
  • 2 cup fresh blueberries
  • 2 lb fresh strawberries Hulled and sliced lengthwise.
  • 1 banana slices Optional for white stripes; use as needed.

Equipment

  • 1 sheet pan

Method
 

Bake and cool the sheet cake
  1. Bake both white cake mixes in a large 12x18 sheet pan (or two 9x13 pans joined together) according to package directions, then cool completely. Make sure the layers are fully cool before frosting to prevent melting.
Make the white buttercream
  1. Beat softened unsalted butter until fluffy, about 3–5 minutes, then gradually add powdered sugar. Keep mixing until the mixture looks lighter and smoother.
  2. Add vanilla extract and 4–6 tablespoons heavy cream, then beat until smooth and spreadable for thick coverage. Stop when the frosting holds soft peaks and spreads without running.
Frost and decorate the American flag design
  1. Frost the entire top of the cooled sheet cake with a thick, even layer of white buttercream. Use an offset spatula for straight, level coverage across the whole surface.
  2. In the upper left corner, arrange fresh blueberries into a dense rectangle to form the canton. Press lightly so the surface stays flat and the blue area looks precise.
  3. Create the red stripes by arranging strawberry slices flat across the length of the cake in neat rows. Keep the spacing uniform so each stripe looks consistent from end to end.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows or by placing thin banana slices. Use a steady hand so the white bands are straight and vivid.
Chill and slice
  1. Refrigerate until ready to serve for 1 hour to set the decorations, then slice into squares. Serve chilled so the fruit and buttercream stay crisp and clean.

Notes

Pro tip: for sharp-looking stripes, make sure the cake is fully cooled and chill the frosted cake 15 minutes before placing strawberries and piping white bands. Store covered in the refrigerator up to 3 days; freezing is not recommended because fresh fruit releases moisture and softens the design. For a dairy-free option, use plant-based butter and a dairy-free heavy cream substitute, keeping the same texture and thickness for smooth spreading.