In a large microwave-safe bowl, combine butter and 1 cup peanut butter. Microwave, uncovered, on high for 1 minute or until butter is melted, stirring once. Beat in confectioners' sugar. Spread into a 13-in. x 9-in. pan coated with cooking spray.
In a microwave, melt candy bars and remaining peanut butter; stir until smooth. Spread over peanut butter layer. Refrigerate until cool.
Cut into 1-1/2-in. x 1-in. bars. Store in an airtight container in the refrigerator.