1Heat oven to 350°F. Grease 13x9-inch pan with shortening or cooking spray.
2In large bowl, beat brown sugar and butter with electric mixer on medium speed until light and fluffy. Beat in peanut butter, vanilla and eggs until well blended. Stir in flour and baking powder. Stir in chocolate chunks. Spread in pan.
3Bake 30 to 35 minutes or until set and golden brown. Cool completely in pan on cooling rack, about 1 hour. Cut into 6 rows by 4 rows.