1 cup butter, room temp
1/2 cup white sugar
1/2 cup brown sugar
1 beaten egg yolk
1 tsp. vanilla
2 cups AP flour
8 Hershey's bars, broken into pieces (I used Special Dark and only 6 bars because I bought a 6 pack)
1/3 cup chopped nuts or toffee bits (I used baking Heath milk chocolate and toffee bits generously sprinkled all over the top, about 3/4 of the bag)
Preheat to 350
In mixing bowl cream together butter and both sugars. When combined add the egg yolk and vanilla, mixing on medium until combined and smooth.
Add flour, 1 cup at a time mixing on low in between each cup to combine.
Dough will almost form a stiff ball.
Press dough onto ungreased cookie sheet about 1/4" thick. Bake 15-20 minutes until edges are golden and center is almost set, but not quite.
As soon as they're done, take them out of the oven and spread the chocolate bars on the top. Let them sit for a minute (they'll start to melt) then spread all over top. Sprinkle with nuts or toffee bits. Put in refrigerator or freezer to harden then cut into triangles.