Make brownies as directed on the box, cool for at least 1 hour. I waited until the bottom of the brownies were cool to the touch
In your stand Mixer add together ⅓ cup butter, peanut butter, powdered sugar, milk and beat until smooth
Spread this mixture over the top of your brownies
In a microwave-safe bowl combine chocolate chips and 3 tablespoons butter
microwave in 30-second intervals until the chocolate chips and butter are smooth, it took about 1.5 minutes for me
cool the chocolate chip mixture for 10 minutes
spread mixture over the peanut butter topping
Sprinkle the top with peanut butter chips and Reese's chunks, press lightly to set (I combined the peanut butter chips and Reese's chunks in a bowl and mixed them before putting them on the brownie so they would spread out evenly)
Refrigerate for as long as you can wait until the mixture is set.