Cream butter & brown sugar, work until light and fluffy. Add beaten egg yolk, vanilla extract & flour
2 Spread thinly on cake sheet and bake at 350 degrees for 15-20 minutes
3 Cut up chocolate into small pieces (food processor will work but be careful not to over chop)
4 Spread over cookie surface as soon as taken out of the oven.
5 Sprinkle with chopped nuts & cut into squares while warm
