In medium microwavable bowl, microwave milk and peanut butter chips uncovered on High 30 seconds. Stir; microwave 30 to 60 seconds longer, stirring every 30 seconds, until smooth and creamy. Stir in peanut butter until smooth. Stir in peanuts and crushed granola bars. Spread over chocolate layer. If peanut butter mixture starts to set, microwave uncovered on High 15 to 30 seconds or until warm and spreadable.