Preheat the oven to 350 degrees. Grease a 13x9x2-inch rectangular pan and set aside. In a medium-size mixing bowl, combine the butter, brown sugar, egg yolk, and vanilla. Stir to mix. Stir in the flour and salt. Press the mixture evenly in the bottom of the prepared pan. Bake until delicately browned, 25 to 30 minutes. The crust will be soft. Remove from the oven and immediately sprinkle the chocolate chips on the crust. Let stand until soft, and then spread the softened chocolate evenly with a knife or rubber spatula. Sprinkle with the nuts. While the cookies dough is still warm, cut into bars. Quantity depends on how large you make the bars.