Preheat oven at 375-degrees. Grease two 9-inch pie pans.
Place dry ingredients in mixing bowl; add butter, egg yolk, and vanilla. Mix with fingers until dough holds together. Divide dough into two balls and press each ball into a pan. Flatten evenly with palms; prick surface all over with floured fork. Slash into wedges.
Bake for 17 to 22 minutes, until the edges are golden brown. Remove from oven. Immediately cut again following slash marks and carefully run the blade around the edge of the crust to loosen the shortbread.
Let shortbread cool. Cut again along slash marks and the crust, then remove wedges to eat. Shortbread keeps in sealed container for several days.
OM NOM NOM!