Heat oven to 350. Grease bottom only of 13 x 9 pan with cooking spray or shortening. (For easier cutting, line pan with foil, then grease foil on bottom only.
In medium bowl, stir brownie mix, pouch of chocolate syrup, water, oil and eggs until well blended. Spread in pan. Bake 28 - 30 minutes or until toothpick inserted 2 inches from side of pan comes out almost lean. Cool completely, about one hour.
In medium bowl, beat filling ingredients (the 1/2 cup of butter, peanut butter, powdered sugar and milk) with electric mixer on medium speed until smooth. Spread mixture evenly over brownie base.
In small microwavable bowl, microwave chocolate chips and the 1/4 cup of butter uncovered on High 30-60 seconds; stir until smooth. Cool 10 minutes; spread over peanut utter layer. Refrigerate a out 30 minutes or until set.
Cut into 9 rows by 4 rows. Store covered in refrigerator.