Source: Cookies and Cups
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
1/3 cup chopped nuts or toffee bits
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 (my friend uses her baking stone and she says it works perfect).
Bake 15-20 minutes until edges are golden and center is almost set, but not quite.
As soon as you remove from the oven spread the broken Hershey pieces and the heat of the cookie will melt them. Spread to cover the entire top of cookie.
Top with your chopped nuts or toffee.
When completely cooled cut into triangle pieces and enjoy!