Go Back

American Flag Cake

American flag cake is a patriotic sheet cake frosted in white buttercream and topped with a crisp blueberry canton and strawberry red stripes. This easy red white blue cake uses boxed white cake mix for a tender crumb and a clean, vivid flag design you can refrigerate and slice into squares.
Print Recipe Pin Recipe
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 box white cake mix Use the ingredients listed on the box (eggs, water, and oil/butter) in addition to the two cake mix boxes.
Buttercream frosting
  • 2 cup unsalted butter Softened.
  • 6 cup powdered sugar
  • 2 tsp vanilla extract
  • 5 tbsp heavy cream Add 4–6 tbsp as needed for spreadable texture.
Flag decorations
  • 2 cup fresh blueberries Keep dry for best placement.
  • 2 lb fresh strawberries Hulled and sliced lengthwise.
  • 1 banana slices Optional—use for white stripes instead of extra frosting if desired.
  • extra white frosting Optional—use for white stripes if you skip banana slices.

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. Cool completely so the frosting won’t melt.
Make the white buttercream
  1. Beat the softened unsalted butter until fluffy, about 2 to 3 minutes. Gradually add the powdered sugar and mix until thick.
  2. Beat in the vanilla extract and heavy cream, adding 4 to 6 tbsp total until the frosting is smooth and spreadable. Stop and scrape the bowl so the texture stays uniform.
Frost and assemble the flag
  1. Spread a thick, even layer of white buttercream over the entire top of the cooled sheet cake. Use an offset spatula to keep the surface level.
  2. In the upper left corner, arrange the fresh blueberries into a dense rectangle to form the canton. Press lightly so gaps don’t show.
  3. Create red stripes by arranging rows of sliced strawberries flat across the length of the cake. Keep the rows uniform and evenly spaced for clean flag lines.
  4. Fill the white stripes by piping extra frosting in rows between the strawberry rows or by placing thin banana slices. Make each white stripe straight and consistent from edge to edge.
Chill and slice
  1. Refrigerate the cake until ready to serve. Slice into squares just before serving for the best clean edges.

Notes

Pro tip: cool the cakes fully before frosting—warm cake will soften buttercream and blur the stripes. Refrigerate covered up to 4 days; freeze unfrosted cake layers up to 2 months, or freeze assembled cake only if needed (texture may soften after thawing). For a lower-sugar option, use a reduced-sugar powdered sugar blend for the buttercream to keep the stripes sturdy while cutting sweetness.