Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a 9×9-inch baking pan, or line it with parchment paper for easy removal.

Prepare the Brownie Layer: In a large bowl, mix the melted butter and sugar together until smooth. Add in the eggs and vanilla extract, and whisk until well combined. In a separate bowl, combine the flour, cocoa powder, salt, and baking powder. Gradually fold the dry ingredients into the wet mixture, stirring until just combined. Pour the brownie batter into the prepared baking pan and spread it out evenly.

Add the Oreo Layer: Place the Oreo cookies on top of the brownie batter, arranging them in a single layer, ensuring the cookies are evenly spaced. Press them gently into the batter.

Make the Cookie Dough Layer: In a medium bowl, beat the softened butter, granulated sugar, and brown sugar together until smooth and creamy. Add the vanilla extract, then mix in the flour and salt. Add the milk a little at a time until the dough comes together and is soft and scoopable. Fold in the mini chocolate chips (if using).

Top with Cookie Dough: Drop spoonfuls of the cookie dough over the Oreo layer, spreading it out as best as you can to cover the surface. It doesn’t need to be perfect – some brownie and Oreo spots can show through.

Bake: Bake for 30-35 minutes, or until a toothpick inserted into the brownie part (not the cookie dough) comes out with just a few moist crumbs. The cookie dough topping will be golden and slightly firm to the touch.

Cool and Serve: Let the brownies cool completely in the pan before cutting them into squares. For extra decadence, serve with a scoop of vanilla ice cream or a drizzle of caramel sauce.