1Cream together the butter and sugar. Add the egg yolk, vanilla, then flour, and mix well.
2Grease cookie sheet, and spread mixture evenly onto it. Bake it at 325 degrees, until it JUST starts to brown (between 5-10 minutes). Allow to cool.
*** trick ***
To help in spreading the dough more evenly, butter or grease your hands a bit first. It will reduce the dough sticking to your hands by quite a bit!
3While cookie is cooling, melt the chocolate chips. I usually do this in a double boiler to avoid burning. When the chocolate is melted and the cookie has cooled some, spread the chocolate onto the cookie evenly. Sprinkle the chopped nuts on top. Place in the refrigerator and allow to cool all the way. cut into squares and serve.