Pour milk into large bowl. Add dry pudding mix. Beat with wire whisk 2 min. or until well blended. Add peanut butter; mix well. Gently stir in whipped topping. Layer one third of the grahams and half the pudding mixture in 13x9-inch dish, breaking grahams necessary to fit. Repeat layers. Top with remaining grahams.
Microwave chocolate and butter in microwavable bowl on HIGH 2 min. stirring after 1 min. Stir until chocolate is completely melted and mixture is well blended. Spread immediately over grahams.
Refrigerate at least 8 hours. Store in refrigerator.
Variation: Prepare as directed, omitting the peanut butter.