1Heat oven to 350°F. In large bowl, mix butter, brown sugar, vanilla and egg yolk. Stir in flour and salt. Press in ungreased rectangular pan, 13x9x2 inches.
2Bake bars 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 bars 30 minutes in pan on wire rack. For bars, cut into 8 rows by 4 rows.