Preheat the oven to 350°F (175°C). Prepare your fudge brownie mix according to the package instructions. Pour the batter into a greased 9×13 inch pan, spreading it evenly. Bake until a toothpick comes out mostly clean, about 25-30 minutes.

Cool the brownies completely on a wire rack. Once cooled, cut them into 1-inch pieces.

Whisk together instant pudding, whole milk, and vanilla extract in a large bowl. Beat for about 2 minutes until the mixture thickens and becomes creamy.

Add the peanut butter to the pudding mixture. Whisk until you achieve a smooth consistency.

Fold in 1½ cups of whipped topping using a spatula.

Layer half of the brownie pieces in a trifle dish. Sprinkle ⅓ of the halved Reese’s cups over the brownies, then spread half of the peanut butter pudding evenly.

Spread 2½ cups of whipped topping over the pudding layer. Repeat with the remaining brownie pieces, Reese’s cups, and peanut butter pudding.

Cover the trifle dish and refrigerate for at least 3-4 hours before serving.