Line a 13" x 9" x 2" pan with a large sheet of aluminum foil, allowing foil to extend 2" out of both ends of dish.
Prepare brownie mix according to package directions, using packets included in package. Bake according to package directions in prepared pan. Cool completely.
Lift foil out of pan. Invert brownies onto a cutting board; remove foil. Cut brownies into 3/4" pieces, using a sharp knife.
Combine vanilla pudding mix and milk in a large mixing bowl; beat at low speed of an electric mixer 2 minutes or until thickened. Add peanut butter and vanilla; beat until smooth. Gently fold in half of whipped cream. Set remaining whipped cream aside (about 1 cup).
Place half of brownies in bottom of a 3-quart trifle bowl; top with 1 1/4 cups chopped peanut butter cup candies and half of pudding. Repeat layers with remaining half of brownies, 1 1/4 cups peanut butter cup candies, and pudding. Pipe or spoon reserved whipped cream over trifle. Garnish, if desired.