Preheat your oven to 350°F (175°C) and grease a 9×9-inch baking pan or line it with parchment paper.

In a medium bowl, whisk together 1 cup of all-purpose flour, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt for the cookie layer. Set aside.

In a large mixing bowl, cream together the 1/2 cup softened unsalted butter, 1/4 cup granulated sugar, and 1/2 cup brown sugar until the mixture is light and fluffy.

Add the egg and 1 teaspoon vanilla extract, mixing until fully incorporated. Gradually fold in the dry ingredients and 1 cup of chocolate chips.

In another bowl, melt 1/2 cup unsalted butter. Stir in 1 cup granulated sugar, then add 2 eggs and 1 teaspoon vanilla extract until blended.

Sift together 1/3 cup cocoa powder, 1/2 cup all-purpose flour, and 1/4 teaspoon salt. Combine these with the wet mixture until smooth.

Pour the brownie batter into the prepared baking pan. Spread the cookie dough on top without mixing.

Sprinkle the chopped Oreo cookies generously atop the cookie layer.

Bake in the preheated oven for 30-35 minutes until the edges are set but the center remains slightly gooey. A toothpick inserted should have moist crumbs.

Let cool in the pan for at least 15 minutes before cutting.