Preheat oven to 350°F.
Make dough from the Reese's Pieces Cookie Mix according to the package directions.
Line a 9x13 baking dish with parchment paper and secure with oven-proof baking clips. Then, put on a pair of vinyl gloves, because the cookie dough will be extremely sticky, and press the cookie dough into the bottom of the pan, making sure to cover the entire bottom of the pan.
Press a layer of 24 Reese's Peanut Butter Cups into the cookie dough.
Prepare the Reese's Brownie mix according to the package directions. Pour the brownie mixture over the Reese's Peanut Butter Cups, and smooth out the mixture using a silicone spatula, making sure to cover all of the peanut butter cups.
Press Reese's Pieces and Reese's Unwrapped Minis into the top on the brownie mixture. Bake in a 350°F oven for 45-50 minutes, until a toothpick inserted in the center should come out with a few moist crumbs.
Remove from the oven, place on a wire rack, and allow to cool completely in the pan.
Yield 24 servings.