1Heat oven to 350°F. Line bottom and sides of 13x9-inch pan with foil, leaving foil overhanging at 2 opposite sides of pan. In large bowl, stir cookie base ingredients until well mixed. Spread into pan; press lightly. Bake 16 to 18 minutes or until set. Cool completely, about 30 minutes.
2In another large bowl, stir together powdered sugar and pudding mix. Add 1/3 cup butter and the milk; beat with electric mixer on medium speed until smooth (filling will be very thick). Spoon over cookie base; press evenly to cover. Refrigerate while making topping.
3In small microwaveable bowl, microwave topping ingredients uncovered on High 1 minute to 1 minute 30 seconds, stirring every 30 seconds until melted and smooth. Spread over filling. Refrigerate uncovered until set, about 30 minutes.
4Use foil to lift bars from pan; pull foil from sides of bars. Cut into 9 rows by 4 rows. Store covered in refrigerator.