Grease a jelly roll pan with butter. Line entire bottom with saltine crackers. in saucepan, melt 2 sticks butter. Stir in 1 cup brown sugar. Boil 3 minutes. Pour over crackers evenly. Bake at 400 degrees for 4 minutes. Sprinkle 2 cups chocolate chips. Spread with knife. Place in freezer until set. Break up into pieces.