MICROWAVE semi-sweet chocolate and milk in microwaveable bowl on MEDIUM 2 min. or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted. Stir in nuts. Spread onto bottom of foil-lined 8-inch square pan.

MICROWAVE white chocolate in separate microwaveable bowl on MEDIUM 1-1/2 min. or until chocolate is almost melted, stirring after 1 min. Stir until chocolate is completely melted. Add peanut butter; stir until melted. Spread over semi-sweet chocolate layer.

REFRIGERATE 2 hours or until firm. Cut into squares.