Preheat your oven to 350°F and line a 9x13-inch baking pan with parchment paper. This prevents sticking and makes cleanup so much easier. I always press the parchment down into the corners, then lightly spray it with cooking spray for extra insurance.

Cream together the softened butter and granulated sugar in a large bowl until the mixture looks pale and fluffy, about 2-3 minutes. You'll know it's ready when you can't see sugar crystals anymore. This step matters more than people realize—it traps air that makes these bars light instead of heavy.

Beat in the eggs one at a time, then add the vanilla bean paste and mix until completely combined. The batter should look smooth and creamy at this point. Don't skip scraping down the bowl between additions—you'll miss unmixed pockets of flour otherwise.

In a separate bowl, whisk together the flour, baking powder, and salt. Gently fold this dry mixture into the wet ingredients along with the milk, alternating between them so everything incorporates evenly. Stop mixing as soon as you don't see streaks of flour—overmixing creates tough bars (I learned that lesson too).

Fold in the sprinkles and white chocolate chips carefully so they distribute throughout without getting crushed. Pour the batter into your prepared pan and spread it evenly with an offset spatula. The 4th of july sugar cookie bars bake best when the batter's distributed to the same thickness everywhere.

Bake for 22-25 minutes, until the top turns light golden brown and a toothpick inserted in the center comes out clean or with just a few crumbs. Don't panic if it looks slightly underdone—it'll continue cooking as it cools. Overbaking turns them dry, so set a timer and don't walk away after minute 20.

Let the bars cool completely in the pan (about 30 minutes), then dust the top with powdered sugar. Cut into 16 pieces using a sharp knife dipped in hot water—this prevents the sprinkles from dragging and tearing. Wipe the knife between cuts for clean edges.