From the Virginia Hospitality Cookbook.
Preheat oven to 350°F.
Cream butter and sugar until light and fluffy.
Mix in egg yolk.
Ad flour gradually, stirring only to blend.
Add vanilla.
Spread about 1/4 inch thick in lightly buttered 10 x 15" jelly-roll pan.
Bake for 20 minutes or until golden brown.
Remove from oven and while still hot distribute chocolate on top.
When chocolate is soft, spread smoothly over surface.
Sprinkle with nuts.
While still warm, cut into bars.
