Preheat oven to 275 degrees F(135 degrees C). Grease 15 1/2 by 10 1/2 inch jelly-roll pan.

Sift the flour, set aside. In a medium bowl, cream the sugar and butter. Add the vanilla and egg yolk; mix well. Stir in the flour. Spread batter evenly into the prepared jellyroll pan.

In a cup, beat egg white slightly; brush over top of dough and sprinkle with nuts.

Bake one hour and 10 minutes or until golden. Immediately cut into 50 bars and remove from pan to cool on wire racks. Store in tightly covered container for at least 3 days before serving.