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Perfect Flag Sheet Cake Recipe with Fresh Berries and Easy Buttercream Frosting

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A simple, moist sheet cake topped with silky buttercream frosting and fresh berries arranged in a patriotic flag design, perfect for summer celebrations and casual get-togethers.

Ingredients

Scale
  • 2 ½ cups (315 g) all-purpose flour
  • 2 ½ teaspoons baking powder
  • ½ teaspoon salt
  • ¾ cup (170 g) unsalted butter, softened
  • 1 ¾ cups (350 g) granulated sugar
  • 4 large eggs, at room temperature
  • 1 tablespoon pure vanilla extract
  • 1 cup (240 ml) whole milk, room temperature (or buttermilk)
  • 1 cup (225 g) unsalted butter, softened (for frosting)
  • 4 cups (480 g) powdered sugar, sifted
  • 1 teaspoon pure vanilla extract (for frosting)
  • 2–3 tablespoons heavy cream or whole milk (for frosting)
  • Pinch of salt (for frosting)
  • About 1 pint fresh strawberries, hulled and halved
  • About 1 pint fresh blueberries
  • Optional: fresh raspberries or blackberries as accents

Instructions

  1. Preheat oven to 350°F (175°C). Grease a 9×13-inch baking pan with butter or non-stick spray and lightly dust with flour, tapping out excess.
  2. In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
  3. In a large bowl, beat softened butter and granulated sugar on medium speed until light and fluffy, about 3-5 minutes.
  4. Beat in eggs one at a time, fully incorporating each before adding the next. Stir in vanilla extract.
  5. Reduce mixer speed to low. Add dry ingredients in three parts, alternating with milk, starting and ending with dry ingredients. Mix each addition just until combined.
  6. Pour batter into prepared pan and spread evenly with a spatula, smoothing the top.
  7. Bake for 35-40 minutes, checking at 35 minutes with a toothpick; it should come out clean or with a few moist crumbs.
  8. Cool cake in pan for 15 minutes, then transfer to a wire rack to cool completely before frosting.
  9. For the buttercream, beat softened butter on medium speed until creamy, about 2 minutes. Gradually add powdered sugar on low speed to avoid clouds.
  10. Add vanilla extract, salt, and 2-3 tablespoons heavy cream or milk. Beat on high for 3-4 minutes until light and fluffy. Adjust consistency with milk if needed.
  11. Spread buttercream evenly over cooled cake using an offset spatula or butter knife.
  12. Arrange halved strawberries in rows on one half of the cake to mimic red stripes, and place blueberries in a rectangular block to represent the blue field. Add optional berries as accents.
  13. Refrigerate cake for at least 30 minutes to set frosting and keep berries fresh. Bring to room temperature about 15 minutes before serving.

Notes

Use room temperature eggs and butter for best blending. Avoid overmixing batter to keep cake tender. If buttercream is too soft, chill for 10 minutes before frosting. Arrange berries gently to avoid juice bleeding. Fresh berries are best; frozen can be used if thawed and drained. Cake can be made a day ahead and stored in fridge; add berries just before serving.

Nutrition

Keywords: flag cake, sheet cake, buttercream frosting, fresh berries, patriotic dessert, summer dessert, easy cake recipe

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