Preheat your oven to 350°F and grease a 9x13 inch baking pan. Line the bottom with parchment paper so the cake releases perfectly — trust me on this one.

Cream together the softened butter and sugar until fluffy, about 3 minutes with an electric mixer. You'll see it turn pale and increase in volume slightly. Add the 3 eggs one at a time, mixing well after each addition.

Pour in the vanilla extract and mix for 30 seconds. Combine the flour, baking powder, and salt in a separate bowl. Alternate adding the dry mixture and milk to your butter mixture, starting and ending with dry ingredients.

Mix until just combined — don't overmix or your cake gets dense. Pour the batter into the prepared pan and smooth the top. Bake for 35 minutes until a toothpick inserted in the center comes out clean.

Cool the cake in the pan for 10 minutes, then turn it out onto a wire rack completely. I always let mine cool for at least 1 hour before frosting, or it'll melt. This step matters more than you think.

Beat the softened butter and powdered sugar together until fluffy, about 2 minutes. Slowly add the heavy cream while mixing, then add a couple drops of red gel coloring. Mix until you get that beautiful pale pink frosting that spreads smoothly.

Frost the entire top of your cooled american flag sheet cake homemade with an offset spatula or butter knife. Arrange fresh strawberries in three horizontal stripes across the top, then fill the remaining space with blueberries in a scattered pattern that mimics stars.