Line a 9 x 9 inch baking pan with foil leaving an overhang on two sides.
Lightly spray foil with nonstick cooking spray.
Beat 1 1/4 cups peanut butter and butter in large mixer bowl until creamy.
Gradually beat in 1 cup powdered sugar.
Stir in remaining 1 cup powdered sugar, 3 cups pretzel pieces and 1/2 cup of chocolate chips.
Press evenly into prepared baking pan.
Microwave the remaining 1 1/2 cups chocolate chips and 3/4 cup peanut butter in microwave-safe bowl for 45 seconds; stir until combined.
If necessary, microwave at additional 10- to 15-second intervals, stirring just until morsels are melted.
Spread chocolate peanut butter layer evenly over powdered sugar mixture. Sprinkle with the remaining pretzel pieces, pressing down lightly.
Refrigerate for at least 3 hours or until firm. Lift from pan; peel off foil and cut into pieces.
Store in a covered container in the refrigerator.