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American Flag Cake

American flag cake is a full patriotic sheet cake frosted in smooth white buttercream and topped with a precise blueberry canton, strawberry red stripes, and white stripes. This red white blue cake is built for easy slicing into squares after a chilled set.
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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
  • 2 boxes white cake mix Use the box directions for eggs, water, and oil as listed.
Buttercream frosting
  • 2 cup unsalted butter Softened to room temperature.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 4 tbsp heavy cream Add 4–6 tbsp total for spreadable consistency.
Flag decorations
  • 2 cup fresh blueberries
  • 2 lb fresh strawberries Hull and slice lengthwise.
  • 1 banana slices or extra white frosting for white stripes Use banana slices or add extra frosting for the white stripe areas.

Equipment

  • 1 sheet pan

Method
 

Bake 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.
  2. Confirm the cake is fully cooled before frosting so the buttercream stays thick and spreadable.
Make the white buttercream
  1. Beat the softened unsalted butter until fluffy, then gradually add the powdered sugar and mix until smooth.
  2. Mix in the vanilla extract, then add heavy cream 1 tablespoon at a time until the frosting is thick but spreadable.
Frost and build the American flag
  1. Spread a thick, even layer of white buttercream over the entire top of the cooled sheet cake.
  2. In the upper left corner, arrange the fresh blueberries in a dense rectangle to form the canton.
  3. Create red stripes by arranging sliced fresh strawberries flat across the length of the cake in even rows.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows or placing thin banana slices.
Chill and slice
  1. Refrigerate the cake until ready to serve, about 1 hour, so the fruit and frosting set cleanly for slicing.
  2. Slice into squares and serve chilled.

Notes

Pro tip: Use a ruler-like spacing for the strawberry rows so your red stripes look uniform from end to end. Refrigerate covered up to 3 days; freeze is not recommended because fresh fruit will soften when thawed. For a lighter option, use light butter or swap part of the buttercream with whipped topping while keeping the frosting thick enough to pipe solid stripes.