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American Flag Cake

American flag cake with a thick white buttercream finish and a crisp blueberry canton with strawberry red stripes. This patriotic sheet cake bakes as one large sheet (or joined pans) and is topped with vivid fruit for an Independence Day cake centerpiece.
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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 boxes white cake mix Use the package ingredients for the eggs, oil, and water.
Buttercream frosting
  • 2 cups unsalted butter Soften at room temperature.
  • 6 cups powdered sugar
  • 2 tsp vanilla extract
  • 5 tbsp heavy cream Use 4–6 tbsp as needed for a smooth, spreadable texture.
Flag fruit decoration
  • 2 cups fresh blueberries For the blueberry canton.
  • 2 lb fresh strawberries Hulled and sliced lengthwise.
  • 0.5 cup banana slices Optional for the white stripes; substitute extra white frosting if preferred.

Equipment

  • 1 sheet pan

Method
 

Bake the sheet cake
  1. Heat oven to the temperature listed on the white cake mix boxes, then bake two white cake mixes in a large 12x18 sheet pan or two 9x13 pans joined together. Bake for the time directed on the box until a toothpick comes out clean, then cool completely.
Make the white buttercream
  1. Beat softened unsalted butter until fluffy, about 2-3 minutes. Scrape the bowl as needed.
  2. Gradually add powdered sugar, then mix until combined and no dry pockets remain. Beat in vanilla extract.
  3. Add heavy cream 1 tablespoon at a time and beat until smooth and spreadable. If it’s too thick, add up to 2 more tablespoons; if too thin, beat in a little more powdered sugar.
Decorate the American flag
  1. Frost the entire top of the cooled sheet cake with a thick, even layer of white buttercream. Use an offset spatula for a flat surface.
  2. In the upper left corner, arrange fresh blueberries in a dense rectangle to form the canton. Press gently so the fruit sits level on the frosting.
  3. Create red stripes by arranging sliced fresh strawberries flat across the length of the cake. Place rows so the slices are uniform from one side to the other.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows, or place thin banana slices if using fruit stripes. Make each white stripe consistent in width.
Chill and serve
  1. Refrigerate until ready to serve for at least 1 hour, uncovered if your frosting is firm enough to avoid surface softening. This helps the fruit set and the slices hold their shape.
  2. Slice into squares and serve chilled, keeping the top fruit pattern visible. Store any leftovers in the refrigerator until used.

Notes

Pro tip: For the cleanest flag look, frost the cake after it’s fully cooled to prevent fruit from sliding. Refrigerate covered for up to 3 days; the cake can be assembled ahead and chilled for best slicing. Freezing is not recommended because fresh strawberries and blueberries soften after thawing. For a lighter option, swap 1:1 of the buttercream’s powdered sugar for a powdered sugar alternative, and use a reduced-fat butter if desired.