• Preheat the oven to 350 degrees F. Line a 9x13-inch baking pan with foil. Spray the foil with cooking spray.  Set it aside.

To make the cookie layer

• In a medium bowl, whisk together the flour, salt, baking soda, and baking powder. Set aside.
• In the bowl of a stand mixer, cream the butter and sugars together until light and fluffy. Add the eggs, one at a time, mixing thoroughly between additions, followed by the vanilla extract.
• Add the dry ingredients, little by little, to the wet. Scrape down the sides of the bowl as necessary. Mix in the chocolate chips.
• Press the cookie dough into the bottom of the prepared baking dish in an even layer. Top with the Oreo cookies, pressing them into the dough slightly.

To make the brownie layer

• Mix the eggs, cocoa powder, salt, baking powder, and vanilla extract together in a medium bowl. 
• Add the granulated sugar to the melted butter and stir until combined. Add the butter/sugar to the cocoa/egg mixture and stir until combined.
• Add the flour, stirring until the flour just disappears and everything is smooth. Spread the brownie batter over the Oreo and chocolate chip cookie layers.
• Bake for 30-35 minutes, or until a toothpick comes out clean when inserted into the center. Cool completely before cutting into squares.