Cream butter and brown sugar; add vanilla and eggs, then walnuts. Add sifted dry ingredients and mix well. Form into 2 to 4 rolls, wrap in waxed paper, and freeze. While still frozen, cut into thin slices and bake on ungreased cookie sheets at 350 degrees F for about 12 minutes. Let cool for about 5 minutes, then remove and cool on newspaper covered with paper toweling.