Ingredients:

  • 1 box (15.25 oz) white or yellow cake mix
  • 3 large eggs
  • 1/2 cup vegetable oil
  • 1 cup buttermilk
  • 8 oz full-fat cream cheese, softened
  • 1/2 cup unsalted butter, softened
  • 4 cups powdered sugar
  • 1 tsp pure vanilla extract
  • 1 pinch salt
  • 1 pint fresh strawberries, hulled and sliced
  • 1 pint fresh blueberries
  • 1 tbsp lemon juice

Instructions:

  1. Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper for a clean release.
  2. Combine the cake mix, eggs, oil, and buttermilk in a mixing bowl. Beat on medium speed for 2 minutes until the batter is smooth and pale.
  3. Pour the batter into the prepared pan and bake for 28-30 minutes until a toothpick inserted in the center comes out clean and the edges begin to pull away from the pan.
  4. Allow the cake to cool completely on a wire rack. Note: Frosting a warm cake will cause the butter to melt and the topping to slide.
  5. In a large bowl, beat the softened cream cheese and butter together until the mixture is pale and fluffy.
  6. Gradually add the powdered sugar one cup at a time, mixing on low speed to prevent sugar from spraying across your kitchen.
  7. Stir in the vanilla extract and salt, then increase the speed to high for 60 seconds to aerate the frosting.
  8. Spread the frosting in an even layer across the cooled cake using an offset spatula.
  9. Toss blueberries and sliced strawberries with lemon juice in a separate bowl until lightly coated.
  10. Arrange the blueberries in the top left corner to create the star field and place the sliced strawberries in horizontal rows to create the red stripes.
  11. Chill the cake in the refrigerator for 3 hours to stabilize the frosting before slicing.