1Heat oven to 350°F. Grease bottom and sides of 13x9-inch pan with shortening or cooking spray.
2In large bowl, beat brown sugar, butter, vanilla and eggs with electric mixer on medium speed, or mix with spoon. Stir in flour and baking powder until well blended. Stir in walnuts and 1 cup baking chips. Spread in pan.
3Bake 25 to 30 minutes or until golden brown and center is set. Cool completely, about 1 hour. Drizzle with melted chips. Let stand until set. For bars, cut into 6 rows by 6 rows.