Let’s bake and assemble these decadent brownies:

1. Preheat Oven and Prepare Pan:

• Preheat your oven to 350°F (175°C), or as directed on your brownie mix package.
• Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two opposite sides to act as handles. Lightly grease the parchment if desired, though usually not necessary with brownies. Set aside.

2. Prepare and Layer Brownie Batter with Reese’s Cups:

• Prepare the brownie mix batter according to the package instructions, using the ingredients (eggs, oil, water) listed on the box.
• Spread about ⅔ of the prepared brownie batter evenly into the bottom of the lined baking pan.
• Arrange the 15 full-size Reese’s Peanut Butter Cups in a single layer over the batter, pressing them in slightly. Space them out evenly.
• Gently spread the remaining ⅓ of the brownie batter over the Reese’s Cups, ensuring they are as fully covered as possible. Spread carefully so as not to displace the candies too much.

3. Bake the Brownies:

• Place the pan in the preheated oven.
• Bake for 25-30 minutes, or until a wooden toothpick inserted into the brownie portion (avoiding a melted Reese’s Cup) near the center comes out with a few moist crumbs attached, but not wet batter. Be careful not to overbake, as this will result in dry brownies.
• If wet batter remains after 30 minutes, bake for a few minutes longer, checking frequently.

4. Cool Brownies Completely:

• Remove the brownies from the oven and place the pan on a wire rack.
• Let the brownies cool completely in the pan. This is crucial and may take 2-3 hours. Do not attempt to frost warm brownies, as the frosting will melt.

5. Make the Peanut Butter Frosting:

• While the brownies cool (or once they are fully cool), prepare the frosting. In a large bowl, beat the room temperature creamy peanut butter and softened unsalted butter together with an electric mixer (handheld or stand mixer) on medium speed until smooth and well combined.
• Gradually mix in the sifted confectioners’ sugar on low speed until incorporated. Scrape down the sides of the bowl as needed. The mixture will be thick at this point.
• Add the heavy cream and vanilla extract. Mix on low speed until combined, then increase the speed to medium-high and whip for about 2 minutes, until the frosting is light, fluffy, and spreadable. If too thick, add a tiny bit more cream; if too thin, add a little more sifted powdered sugar.

6. Frost and Finish the Brownies:

• Once the brownies are completely cool, use the parchment paper overhang to carefully lift them out of the pan and place them on a cutting board.
• Spread the prepared peanut butter frosting evenly over the top of the cooled brownies.
• Sprinkle with optional mini chocolate chips or crushed peanut butter cups. Add an optional chocolate drizzle if desired.

7. Chill (Optional but Recommended) and Serve:

• For the neatest slices and best texture, chill the frosted brownies in the refrigerator for at least 30 minutes to 1 hour to allow the frosting to set.
• Slice into squares and serve. Enjoy!

Patience during cooling is key for frosting and slicing!