Preheat your oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving a little overhang on the sides for easy removal. Mix your dry ingredients first—whisk together flour, cocoa powder, baking powder, and salt in a medium bowl. Set this aside because we're tackling the wet ingredients next.

Melt your butter in a large saucepan over medium heat, then stir in sugar. Remove from heat and let it cool for about 2 minutes—this prevents scrambling your eggs. Whisk in the eggs one at a time, then add vanilla extract and mix until everything's smooth and combined.

Fold the dry mixture into the wet ingredients using a spatula, stirring until just combined. Don't overmix because that's how you get tough brownies instead of fudgy ones. Fold in the chocolate chips so they're evenly distributed throughout the batter.

Pour the batter into your prepared pan and spread it evenly with a spatula. Bake for 22-25 minutes until a toothpick inserted in the center comes out with just a few moist crumbs. The top should look set but still kinda soft—trust me, it'll continue cooking as it cools.

Let the brownies cool completely in the pan, then pop them in the freezer for at least 30 minutes. This makes them way easier to cut into shapes and stack without falling apart. I learned this the hard way after my first batch turned into brownie chunks instead of neat rectangles.

Cut the cooled brownies into 24 rectangles (about 2x3 inches each)—you'll have 12 pairs for sandwiches. Lay half of them on a parchment-lined baking sheet. This is where the magic happens: quickly spread a thin layer of vanilla ice cream on 12 brownie pieces.

Top the vanilla layer with strawberry ice cream, then blueberry ice cream, creating that gorgeous red-white-blue effect. Cap each with another brownie rectangle and freeze for at least 2 hours before serving. The patriotic brownie ice cream sandwiches are now ready to absolutely steal the show at your summer gathering.