1.Preheat oven to 350� F.
2.For Brownies:
3.Microwave butter and baking bars in small, microwave-safe bowl on HIGH(100%) power for 1 minute; stir.
4.Microwave at additional 10 to 20 second intervals, stirring until smooth.
5.Beat granulated sugar and eggs in large mixer bowl until thick and lemon coloured.
6.Beat in flour and melted chocolate mixture.
7.Pour into ungreased 15 x 10-inch jelly-roll pan.
8.Bake for 24 to 28 minutes or until set.
9.Cool completely in pan on wire rack.
10.For Filling:
11.Beat peanut butter and butter in medium mixer bowl until creamy.
12.Add powdered sugar and milk; beat on low speed until well mixed.
13.Spread over cooled brownie layer.
14.Cover; cool slightly before adding topping.
15.For Topping:
16.Microwave morsels and vegetable shortening in small, heavy-duty plastic bag on HIGH (100%) power for 30 seconds; knead.
17.Microwave at additional 10 to 20 second intervals, kneading until smooth.
18.Cut tiny corner from bag; squeeze to drizzle over peanut butter layer.
19.Refrigerate for 1 hour or until chocolate is set.
20.Cut into bars.
21.Store tightly covered in refrigerator.
22.Makes about 5 dozen bars