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American Flag Cake

American flag cake with a thick white buttercream layer and a crisp fruit flag design using a blueberry canton and strawberry red stripes. This patriotic sheet cake is baked, cooled, frosted, then chilled so the fruit and frosting rows stay clean and vivid.
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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: 380
Ingredients Equipment Method Notes

Ingredients
  

White cake
  • 2 boxes white cake mix Use the ingredients called for on the boxes (typically eggs, oil, and water).
  • 1 ingredients called for on cake mix boxes Add only what the box specifies; this keeps the cake’s bake time and texture consistent.
Buttercream frosting
  • 2 cups unsalted butter Softened for smooth spreading.
  • 6 cups powdered sugar Gradually added to prevent lumps.
  • 2 tsp vanilla extract
  • 4 tbsp heavy cream Use 4–6 tbsp as needed for spreadable consistency.
Flag decoration
  • 2 cups fresh blueberries For the dense upper-left canton.
  • 2 lb fresh strawberries Hulled and sliced lengthwise for uniform red stripes.
  • 1 banana slices or extra white frosting for white stripes Use banana slices for classic contrast, or pipe extra frosting for white stripes.

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) following package directions, then remove and cool completely at room temperature.
  2. Let the cakes cool fully before frosting so the buttercream stays thick and the fruit rows won’t slide.
Make the white buttercream
  1. Beat the softened unsalted butter until fluffy, about 2–3 minutes, then gradually add the powdered sugar while mixing until combined.
  2. Add vanilla extract and 4 tablespoons heavy cream, then beat until smooth and spreadable, adding more heavy cream as needed from 4–6 tablespoons total.
Frost and decorate 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 fresh blueberries in a dense rectangle to form the canton.
  3. Create red stripes by arranging rows of sliced lengthwise strawberries flat across the length of the cake.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows or by placing thin banana slices.
  5. Refrigerate the decorated cake until ready to serve, about 1 hour, to set the frosting and keep the fruit design crisp.
Slice and serve
  1. Slice into squares and serve chilled, with the flag pattern still intact.

Notes

Pro tip: for clean stripes, slice strawberries to a consistent thickness and keep the cake fully cooled before frosting. Refrigerate covered up to 3 days; freeze is not recommended because the fresh fruit texture can soften when thawed. For a lighter option, swap part of the buttercream (about half the butter) with a high-quality Greek yogurt frosting base, then chill well to maintain firm stripes.