Preheat your oven to 350°F and line a standard 9x13-inch sheet pan with parchment paper. Cream together 1/2 cup butter and 1 1/2 cups sugar until it's light and fluffy—this takes about 3 minutes with an electric mixer. The mixture should look pale and almost doubled in volume when you're done.

Add your 3 eggs one at a time, beating for about 30 seconds between each addition. Pour in 1 tsp vanilla powder and mix until everything is fully combined and smooth throughout the batter.

In a separate bowl, whisk together 2 cups flour, 1 tsp baking powder, and 1/2 tsp salt. Alternate adding the dry mixture and 1 cup milk to the wet ingredients, starting with dry and ending with dry. Mix just until combined—don't overmix or your cake gets tough.

Divide your batter evenly into 3 bowls. Leave one plain for the white layer, stir 1 tsp red food coloring into the second, and 1 tsp blue food coloring into the third. Personally, I've found that mixing the colors for exactly 10 seconds gives you the most vibrant results without overdoing it.

Pour the batters into your prepared pan in three separate sections (white, red, blue), then gently swirl them together with a knife to create a marbled flag effect. Don't stress about making it perfect—the frosting covers any imperfections anyway.

Bake for 30 minutes until a toothpick inserted in the center comes out clean or with just a few crumbs. The cake should spring back when you touch the top and have a light golden color on the edges. Let it cool completely in the pan before frosting.

For your cream cheese frosting, beat 8 oz cream cheese and 1/4 cup butter together for 2 minutes until smooth and creamy. Gradually mix in 1 cup powdered sugar and spread the frosting over your cooled american flag sheet cake crowd. Top with 1/4 cup rainbow sprinkles for extra patriotic flair.