Prepare brownie mix according to package directions. For each cupcake cup spread 1 teaspoon of peanut butter over 2 Oreo cookies and stack them on top of each other. Place oreo stacks into the cupcake lined muffin cups. Spoon 2 tablespoons of brownie batter over each stacked oreos and let it run down the sides of the cookies. If you have left over brownie batter, bake separately in a separate baker or muffin tin. Bake cookies and brownies for 18 to 20 minutes, until brownies are cooked through. Let cool completely then serve.