Preheat oven to 325 degrees. 11 x 17 cookie sheet with sides (may be lined with foil)

Cream butter, sugar; beat in yolk and vanilla. Beat in dry ingredients. Press dough in pan (may line pan with foil). Brush with egg white. Sprinkle with nuts and press in.

Bake for 35 minutes. Remove and immediately cut in squares, diamonds or rectangles. Gets crisp quickly.

Cool.