Preheat the oven to 350ºF. Spray a 9x13-inch baking dish with nonstick cooking spray, or line with parchment paper or foil. (If using foil, spray it with nonstick cooking spray.)

In a large bowl, combine the melted butter, 2 1/2 cups sugar, vanilla and eggs. Mix well. Stir in the flour, cocoa powder and salt. Mix until fully combined. Set aside.

In another bowl, combine the cream cheese, 1/3 cup sugar and egg. Beat until well combined and smooth.

Roughly chop the Oreo cookies and the cookies and cream bar.

To the cream cheese filling, stir in the chopped Oreos and the cookies and cream bar.

Spread 2/3 of the brownie mixture into the prepared baking dish. It is thick, so using an offset spatula will help. Drop the cream cheese mixture over the top of the brownie layer, spreading into an even layer. Drop the remaining brownie mixture over the top in dollops, then carefully spread the brownie layer over the top.

Bake the brownies in the preheated oven until a tester inserted in the middle comes out clean, about 45 minutes.

Cool completely before cutting into bars. Store any leftovers in the refrigerator.