Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan with non-stick spray or line it with parchment paper.
In a large mixing bowl, combine the melted butter and granulated sugar. Stir until the mixture is smooth and well-combined.
Beat in the eggs, one at a time, and add the vanilla extract until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Fold in the chocolate chips for extra richness. The batter will be thick.
Pour about two-thirds of the brownie batter into the prepared baking pan, spreading it evenly to cover the bottom.
Carefully place the Oreo cookies, evenly spaced, on top of the brownie layer.
Spoon the remaining brownie batter over the Oreos, ensuring they are fully covered.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (but not wet batter).
Allow the brownies to cool in the pan for at least 20 minutes before slicing them into squares.
Notes
Serve warm with vanilla ice cream and chocolate sauce. Garnish with crushed Oreos for added flair!