Pre heat oven to 350 and place rack in center of oven.
Beat butter and brown sugar until combined. Add cornstarch, flour, salt, vanilla and one cup chopped nuts. Mix just until combined.
Press mixture into a greased jelly roll pan or other large cookie sheet, the dough should measure about 12x14 in the pan. I used a small floured rolling pin to spread the dough evenly once it was patted out in the pan. Then I formed the edges of the dough with my hands.
Bake for about 20 minutes, or just until edges are slightly golden brown.
Remove from oven and immediately place chocolate chips on top of shortbread. Let stand for a few minutes, and then spread chocolate until cookie layer is covered. Sprinkle immediately with nuts.
Let cool until chocolate is set and cookie is completely cooled.
Break or cut up and enjoy.
Notes
-You may set the pan in the fridge to cool faster.-If you are storing for later use, and want to remove from pan, layer the pieces with wax or parchment paper in between.