1 cup (2 sticks) butter, room temperature
Preheat oven to 350 degrees Fahrenheit. Grease a 9 x 13-inch baking pan with cooking spray, line with wax paper and grease again (this will help the wax paper stick to the pan and stay put).
Cream the butter and both sugars in a large bowl with an electric mixer on medium speed for 3-5 minutes. Add the eggs and vanilla and mix well to thoroughly combine. In a separate bowl, whisk together the flour, baking soda, salt and espresso powder, then slowly incorporate into the mixer until just combined. Stir in the peanut butter chips and 2 ounces of the chocolate chips. Spread the cookie dough in the bottom of the baking dish with your fingers (get them wet to prevent sticking). Top with a single layer of Oreos. Mix together brownie mix, adding in the chocolate chips. Pour the brownie batter over the cookie dough and Oreos spreading in an even layer. Cover with foil and bake for 30-35 minutes. Remove foil and continue baking for an additional 20-30 minutes. Let cool completely before cutting — brownies may still be gooey in the middle when still warm, but will set once cooled. Serve with ice cream, hot fudge and/or whipped cream.
To halve this recipe for an 8×8 brownie mix, simply half the cookie dough ingredients. Also, you can vary this recipe by changing the cookie dough flavor. We think this would be amazing with plain old peanut butter cookie dough.