Preheat oven to 275 F. Spray a small quarter sheet baking pan (15x10-inch or slightly smaller) with baking spray.
In the bowl of a stand mixer, combine flour, sugar, butter, vanilla, and egg yolk. Beat until blended well, scraping down the sides as needed. Turn the dough out into the prepared baking sheet and press with the palms of your hand to even out.
In a small bowl, beat the egg white and brush it on top of the prepared dough. Add chopped pecans (or any other type of nut).
Bake for one hour, or until golden.
Cut into strips immediately before the bars harden. Cool on a wire rack.
