Ingredients:

  • 2 1/4 cups (280g) all-purpose flour
  • 1 1/2 cups (300g) granulated sugar
  • 1 tsp (5g) baking soda
  • 1/2 tsp (3g) salt
  • 1 cup (240ml) buttermilk, room temperature
  • 1/2 cup (120ml) vegetable oil
  • 2 large eggs, room temperature
  • 1 tsp (5ml) pure vanilla extract
  • 1 cup (225g) unsalted butter, softened
  • 4 cups (500g) powdered sugar, sifted
  • 2 tbsp (30ml) heavy cream
  • 1 tsp (5ml) pure vanilla extract
  • 1g salt
  • 1 cup (150g) fresh blueberries
  • 2 cups (250g) fresh raspberries or sliced strawberries

Instructions:

  1. Preheat oven to 350°F (175°C) and line a 10x15 inch sheet pan with parchment paper.
  2. Whisk together all-purpose flour, granulated sugar, baking soda, and salt in a large bowl.
  3. Fold in buttermilk, vegetable oil, eggs, and vanilla extract; stir until the batter is smooth and ribbon-like.
  4. Spread batter evenly into the prepared pan and bake for 22-25 minutes until the center springs back and a toothpick comes out clean.
  5. Allow the cake to cool completely in the pan.
  6. Whip softened butter and powdered sugar until light and airy, then beat in heavy cream, vanilla extract, and salt until firm and spreadable.
  7. Smooth a thick layer of buttercream across the cake surface and chill in the refrigerator for 60 minutes to set.
  8. Create the flag design by pressing blueberries into the top-left corner for the union and alternating rows of raspberries and bare buttercream for the stripes.