Melt ½ cup of unsalted butter in the microwave for about 30 seconds and let it cool slightly. Stir in ½ cup of brown sugar and ¼ cup of white granulated sugar, mixing well. Add 1 tsp of pure vanilla extract and 1 large egg, combining until smooth. Set aside.

Whisk together 1 ½ cups of all-purpose flour, ½ tsp of baking powder, ½ tsp of baking soda, and a pinch of salt in a separate bowl. Gently fold this dry mixture into the brown sugar mixture. Add ½ cup of chocolate chips and 1 cup of Oreo pieces, set aside.

Melt 4 oz of semi-sweet chocolate in a heatproof bowl over simmering water, stirring until smooth. Cool for 5 minutes, then mix in ½ cup of unsalted butter, ½ cup of brown sugar, ¼ cup of white granulated sugar, and 1 tsp of vanilla extract. Add 1 large egg and blend until combined.

Incorporate the dry ingredients for the brownie layer by whisking together ½ cup of all-purpose flour, 2 tbsp of unsweetened cocoa powder, ¼ tsp of baking powder, and a pinch of salt. Gradually fold this into the melted chocolate mixture. Add ½ cup of chocolate chips, ½ cup of Oreo pieces, and ¼ cup of Oreo crumbs.

Chill the brownie cookie dough in the refrigerator, covered, for about 10-15 minutes. Prepare cookie sheets by lining them with parchment paper.

Scoop portions of both Oreo chocolate chip and brownie cookie doughs, rolling them into balls. Combine by swirling and pinching together to create a marbled effect. Place on the prepared baking sheet.

Preheat oven to 350°F (175°C) and bake cookies for 13-15 minutes until lightly golden on edges and slightly underbaked in the center. Cool on baking sheets for a few minutes before transferring to a wire rack.

Enjoy the Oreo brookies! Delight in the contrast of fudgy brownie and crunchy Oreos, perfect with cold milk or ice cream.