Preheat your oven to 350°F (175°C). Grease your 9x13 inch baking pan or line it with parchment paper for easy removal.
In a medium saucepan over low heat, melt the 1 cup of butter completely, then remove from heat and let it cool slightly.
In a large mixing bowl, whisk together 2 1/4 cups granulated sugar and 4 large eggs until the mixture is smooth and glossy.
Stir in 1 1/4 cups unsweetened cocoa powder, 1/2 teaspoon salt, and 1 teaspoon baking powder into the egg and sugar mixture until well combined.
Add 2 teaspoons vanilla extract and 1 1/2 cups all-purpose flour to the mixture, stirring until just combined. Avoid overmixing for that fudgy texture.
Fold in 1 cup semi-sweet chocolate chips, ensuring they are evenly distributed throughout the brownie batter.
Pour half of the brownie batter into the prepared baking pan. Place 1 package of double-stuffed Oreos in a single layer on top of the batter. Pour the remaining brownie batter over the Oreos, spreading it evenly.
Bake in the preheated oven for about 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan on a cooling rack. Once cool, use the white frosting in a tube to decorate the top as desired.
