Preheat the oven to 350°F (175°C). Grease and line a 9x13 inch baking pan with parchment paper.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In another bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, alternating with the milk, and mix until just combined.

Pour the batter into the prepared baking pan and smooth the top.

Bake for 30 minutes or until a toothpick inserted in the center comes out clean. Let cool completely.

In a mixing bowl, beat the softened butter until creamy. Gradually add the powdered sugar, mixing until smooth.

Add the vanilla extract and milk, and beat until fluffy.

Spread a layer of frosting over the cooled cake.

Arrange the sliced strawberries in the shape of the flag's stripes and place blueberries in the top left corner for the stars.

Optionally, sprinkle coconut flakes for additional decoration.