1Heat oven to 350°F. Spray 13x9-inch pan with cooking spray. In large bowl, mix butter, brown sugar, vanilla and egg yolk. Stir in flour and salt. Press in pan.
2Bake 25 to 30 minutes or until very light brown (crust will be soft). Immediately sprinkle chocolate chips on hot crust. Let stand about 5 minutes or until chocolate is soft; spread evenly. Sprinkle with nuts.
3Cool 30 minutes in pan on cooling rack. For bars, cut into 8 rows by 4 rows.