I loved how the house smelled when my Mom baked these at Christmas time. I still remember her smoothing out the chocolate, and absolutely loved that after she cut them, she let Kris and I eat the edges right out of the pan.
Preheat oven to 350°.
Mix sugar, butter, egg yolk, and vanilla.
Stir in flour and salt.
Press into a greased 9x13" pan.
Bake until very light brown, about 25 minutes.
Remove from oven, and break chocolate over hot crust, letting melt.
Spread chocolate around to cover.
Top with nuts, if desired.
Cool and cut into bars.