Preheat the oven to 350°F. Lightly grease a 12x9-inch baking pan.

Prepare the fudge brownie batter according to the package directions. Spread the batter evenly into the prepared baking pan.

Bake for 20 to 25 minutes, or until a toothpick inserted near the center comes out with moist crumbs rather than wet batter.

Transfer the pan to a wire rack and allow the brownies to cool completely. Once cooled, cut the brownies into approximately ¾-inch pieces.

Cut the miniature Reese’s peanut butter cups in half. Reserve a portion of them for decorating the top of the dessert.

Pour the cold milk into a large mixing bowl and add the instant vanilla pudding mix. Whisk or beat for about 2 minutes, until the pudding becomes smooth and noticeably thickened.

Add the creamy peanut butter and vanilla extract to the pudding. Mix until completely combined and smooth.

Gently fold 1½ cups of the thawed whipped topping into the peanut butter pudding mixture until evenly incorporated.

Arrange one-third of the brownie pieces in the bottom of a large 5-quart glass trifle bowl.

Scatter some of the peanut butter cup pieces over the brownies, then spread one-third of the peanut butter pudding mixture over the top.

Repeat the brownie, peanut butter cup, and pudding layers until all three layers have been assembled.

Spread the remaining whipped topping over the top of the trifle.

Garnish with the reserved Reese’s peanut butter cups.

Refrigerate until chilled and set. Serve cold and keep any leftovers refrigerated.