Line the bottom and sides of a jelly roll pan with aluminum foil. Place 20 graham cracker squares (split in half) on the foil. Put 2 sticks of butter and 3/4 c. sugar in a pan and boil exactly 2 minutes. Pour over the crackers. Sprinkle with 2/3 c. crushed walnuts. Bake 350° for exactly 10 minutes. Cool. Melt 6 oz. chocolate chips and pour over.