Step 1: Prepare the Baking Pan

1. Preheat your oven to 350°F (175°C).
2. Line a 9×9-inch square baking pan with parchment paper, leaving an overhang on the sides for easy removal. Lightly grease the parchment with butter or nonstick spray.

Step 2: Make the Cookie Dough Layer

1. In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.
2. Add the egg and vanilla extract, mixing until fully incorporated.
3. In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
4. Fold in the chocolate chips using a spatula.
5. Press the cookie dough evenly into the prepared baking pan to form the bottom layer.

Step 3: Add the Oreo Layer

1. Arrange the Oreo cookies in a single layer on top of the cookie dough, pressing them down slightly. It’s okay if the Oreos don’t cover the entire surface—just space them evenly.

Step 4: Make the Brownie Batter

1. In a medium bowl, whisk together the melted butter and granulated sugar until smooth.
2. Add the eggs and vanilla extract, whisking until the mixture becomes glossy and slightly thickened.
3. Sift in the cocoa powder, flour, baking powder, and salt. Fold the dry ingredients into the wet ingredients using a spatula until just combined. Avoid overmixing to keep the brownies fudgy.

Step 5: Assemble the Oreo Brookies

1. Pour the brownie batter over the Oreo layer, spreading it evenly with a spatula to cover all the cookies.

Step 6: Bake

1. Bake the Oreo Brookies in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter).
2. Remove from the oven and let cool completely in the pan on a wire rack.

Step 7: Slice and Serve

1. Once fully cooled, lift the brookies out of the pan using the parchment paper overhang. Slice into 16 squares or bars.
2. Serve and enjoy!