Prepare brownie mix according to package directions. Make sure not to over bake the brownies. Cool on a wire rack; cut into 1/2-inch pieces.

Cut 1 ½ bags of peanut butter cups in fourths. Cut remaining cups in half; set aside for garnish.

In a large-sized bowl, whisk milk and pudding mixes for 2 minutes. Add peanut butter and vanilla; mix well. Fold in 1-1/2 cartons whipped topping.

Place a third of the brownies in a very large-sized bowl. Top with a third of the remaining peanut butter cups. Spoon a third of the pudding mixture over the top. Repeat layer ensuring remaining brownies, cups, and pudding mixture. are mixed. 

Cover with remaining whipped topping; garnish with reserved peanut butter cups.

Refrigerate until chilled.