Line a 9x9-inch pan with aluminum foil.

Melt 5 Tbl. butter in a large microwave-safe bowl. Stir in peanut butter, brown sugar and confectioners sugar. Press into prepared pan and chill.

Melt remaining 5 Tbl. butter and chocolate chips in a microwave-safe bowl in microwave for 1 minute. Stir, heat in 30-second increments until smooth. Pour over peanut butter base.

Chill until firm, at least two hours or overnight. Cut into bars, about 1 1/2-inch square. Store in refrigerator.