Preheat oven to 350 degrees F. Coat a 9×13 pan with cooking spray and set aside.
Prepare the brownie batter according to package directions (do not bake). Spread the batter in pan and set aside. In a large bowl, beat cream cheese with a stand or hand-held mixer using the whisk attachment until free of lumps. Add condensed milk and peanut butter and beat until smooth. Stir in the Reese’s Pieces candies. Carefully spoon the mixture over the batter and spread evenly.
Bake for 40 minutes in the preheated oven, or until the cheesecake layer is set and golden brown. Refrigerate for 30 minutes.
In a small microwave-safe bowl, heat the chocolate chips and whipping cream for 1 minute. Stir until smooth, heating in 15-second intervals if needed. Spread over the cheesecake layer and sprinkle Reese’s Peanut Butter Cup pieces over top. Store covered in the refrigerator.
Notes
If you can't find a 19.5-oz. box of brownie mix, buy the largest size you can find. Sometimes the box will say "9x13" on the front.
Prepare the brownie batter, but DO NOT BAKE IT until the cheesecake batter has been spread over the top. The brownie and cheesecake batters get baked together, at the same time.
It's ok if the cheesecake layer does not spread all the way to the sides. It'll be a relatively thin layer before it's cooked, but will puff up nicely after you pull it out of the oven.
Get extra Reese's Pieces to sprinkle on top, for an extra bit of fun. Also, did you know that you can now buy Reese's Peanut Butter Cups that have Reese's Pieces hiding inside? It's a dream come true!
I have 12 servings listed on the recipe card, but these are super-rich so I recommend cutting them into even smaller pieces when serving them at gatherings.
Be prepared for Reese's Cheesecake Brownies to be your new favorite dessert!