Line a 15x10x1 inch jelly roll pan with waxed paper and grease the paper. Arrange graham crackers in pan and set aside. In a saucepan, melt butter and sugar over medium heat; let boil gently for 3 minutes. Spread evenly over graham crackers. Sprinkle nuts on top. Bake at 325 for 10 minutes. Cool. Meanwhile, melt chocolate chips; spread over bars and allow to cool again. After chocolate is set, pan can be turned over so waxed paper can be peeled off. Bars can be frozen. Yield 4 dozen.