Preheat the oven to 350°F (175°C).
Grease and line a 9×13-inch sheet pan.
Whisk together the flour, baking powder, and salt.
Beat the butter and sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Mix in the vanilla extract.
Alternate adding the dry ingredients and milk until fully combined.
Pour the batter into the prepared pan and spread evenly.
Bake for 28–32 minutes or until a toothpick comes out clean.
Let the cake cool completely.
Whip the heavy cream, powdered sugar, and vanilla until stiff peaks form.
Spread the whipped frosting evenly over the cooled cake.
Arrange blueberries in the upper-left corner to resemble the stars section of the flag.
Create alternating red and white stripes using rows of sliced strawberries and exposed frosting.
Chill for 30 minutes before serving.
Slice and enjoy your patriotic dessert.
