Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking dish or line it with parchment paper.

In a mixing bowl, combine melted butter and granulated sugar until smooth. Add eggs and vanilla, mixing well. Sift in cocoa powder, flour, salt, and baking powder, stirring until just combined. Pour this batter into your prepared pan and spread evenly.

In another bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy. Beat in the egg and vanilla until well incorporated. Gradually add flour, baking soda, and salt, mixing until just combined. Fold in the crushed Oreos gently.

Drop spoonfuls of the cookie mixture over the brownie base, allowing it to spread while baking.

Bake for about 25-30 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs.

Let them cool completely in the pan before slicing into squares. Serve warm for an extra gooey treat.