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American Flag Cake

American flag cake is a patriotic sheet cake frosted in thick white buttercream, then topped with a blueberry canton and strawberry red stripes. This red white blue cake uses clean, vivid fruit rows so the design looks crisp from edge to edge.
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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 mix
  • 2 box white cake mix Use ingredients listed on the box for eggs, oil, and water.
frosting
  • 2 cup unsalted butter Softened.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 5 tbsp heavy cream Add 4–6 tbsp as needed to reach spreadable consistency.
decoration
  • 2 cup fresh blueberries
  • 2 lb fresh strawberries Hulled and sliced lengthwise.
  • 0.5 cup banana slices or extra white frosting for white stripes Choose banana slices or use extra frosting for the white stripes.

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 a toothpick inserted in the center comes out clean.
  2. Cool the baked cakes completely before frosting. Let the cakes cool on the pan(s) until fully at room temperature so the buttercream won’t melt.
Make the white buttercream
  1. Beat softened unsalted butter until fluffy. Use medium speed and stop when the butter looks lighter in color and airy.
  2. Gradually add powdered sugar, then mix until combined. Pause to scrape the bowl as needed for an even texture.
  3. Add vanilla extract and beat until smooth. Mix just until the frosting tastes uniformly vanilla.
  4. Add heavy cream, 1 tablespoon at a time, and beat until the frosting is smooth and spreadable. Stop when you can spread it in a thick layer without it running.
Frost and decorate the American flag
  1. Frost the entire top of the cooled sheet cake with a thick, even layer of white buttercream. Spread to the edges for a clean base for the fruit pattern.
  2. Arrange fresh blueberries in a dense rectangle in the upper left corner to form the canton. Pack them tightly so the blue area looks solid and precisely filled.
  3. Create red stripes by arranging sliced fresh strawberries flat across the length of the cake in uniform rows. Keep the rows parallel so the pattern stays crisp.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows or placing thin banana slices. Add enough so the white lines are clearly visible from above.
Chill, slice, and serve
  1. Refrigerate the decorated cake until ready to serve. Chill for at least 1 hour so the frosting sets and the fruit holds its rows.
  2. Slice into squares and serve chilled. Use a clean cut for each piece so the flag design remains intact.

Notes

Pro tip: cool the cake completely before frosting—warm cake will make buttercream slide and blur the fruit lines. Store covered in the refrigerator for up to 3 days; freeze unfrosted baked cake layers only (up to 2 months) and frost after thawing. For a lighter option, use a reduced-fat butter and swap 3 cups powdered sugar for 3 cups confectioners’ sugar with no-sugar-added sweetener if your frosting texture holds well.