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American Flag Cake

American flag cake made with boxed white cake mix baked in a sheet pan, then frosted with thick, smooth buttercream and topped with a crisp blueberry canton and strawberry red stripes. This patriotic sheet cake uses fruit rows plus white frosting (or banana) stripes across the full surface for a clean 4th of July cake 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: 520
Ingredients Equipment Method Notes

Ingredients
  

white cake mix
  • 2 boxes white cake mix Use the ingredients on the boxes (eggs, water, and oil) for the full mix instructions.
frosting
  • 2 cup unsalted butter Softened.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 4 tbsp heavy cream Add 4–6 tbsp total to reach spreadable thickness.
decoration
  • 2 cup fresh blueberries
  • 2 lb fresh strawberries Hulled and sliced lengthwise.
  • 0.5 cup banana slices Optional: use banana slices for the white stripes, or use extra white frosting instead.

Equipment

  • 1 sheet pan

Method
 

Bake the sheet cake
  1. Heat oven to 350°F and bake both white cake mixes in a large 12x18 sheet pan (or two 9x13 pans joined together) according to package directions. Bake until the centers spring back and a toothpick comes out clean, then cool completely.
Make the buttercream
  1. Beat the softened unsalted butter until fluffy, about 2 to 3 minutes at room temperature. Gradually add powdered sugar, then mix in vanilla extract and heavy cream until smooth and spreadable.
Frost the cake
  1. Spread a thick, even layer of white buttercream over the entire top of the fully cooled sheet cake. Use an offset spatula to smooth the surface for sharp fruit lines.
Decorate as an American flag
  1. In the upper left corner, arrange the fresh blueberries into a dense rectangle to form the canton, pressing lightly so they adhere to the frosting. Keep the rectangle edges clean for a clear flag shape.
  2. Create the red stripes by arranging rows of sliced strawberries flat across the length of the cake. Place each row evenly so the stripes stay uniform from edge to edge.
  3. Fill the white stripes by piping extra frosting in rows between the strawberry rows or placing thin banana slices. Make sure the white rows are continuous and reach the cake edges.
Chill and slice
  1. Refrigerate the decorated cake until ready to serve, about 1 hour, so the buttercream sets and the fruit firms up. Slice into squares right before serving for best texture.

Notes

Pro tip: cool the cake completely before frosting—warm cake causes buttercream to melt and slide, blurring the flag lines. Refrigerate covered up to 3 days; the fruit topping is best within that window. Freezing isn’t recommended because fresh strawberries and blueberries can weep after thawing. For a simpler swap, use all extra white frosting instead of banana slices to keep the stripes purely dairy-based.