Mix margarine, brown sugar, vanilla and egg yolk in large bowl. Stir in flour and salt. Press dough in ungreased rectangular pan, 13 x 9 x 2 inches.
Bake 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 soft; spread evenly. Sprinkle with nuts. Cool 30 minutes in pan on wire rack. Cut into 2 x 1-1/2-inch bars while warm.