Preheat oven to 350 degrees. Line a 9x13 inch metal pan with nonstick foil or parchment paper.

Cut the butter up and put it in a bowl, and with an electric mixer beat the butter and brown sugar until creamy. Add the egg, vanilla and salt; beat until mixed.

Stir in flour and ½ cup chopped nuts. Spread evenly in the pan, pressing tightly to make crust.

Bake for 25 minutes or until lightly browned. Pull from oven and immediately sprinkle chopped chocolate over the top. Let the chocolate sit for about 5 minutes to soften, then gently spread it across the shortbread base.

Sprinkle remaining nuts over the top. Allow bars to cool, then put in the refrigerator to set chocolate. Lift from pan and cut into desired bar size.

Note: To toast the walnuts, spread them on a baking sheet and bake at 350 for about 8 minutes or until they start to release their oils (appear shiny, aromatic).