Melt butter and water over med. High heat. Add sugar and salt and stir with wooden spoon while bringing to a boil. Boil until it loses it's yellow color and looks white, then mix in 1 cup walnuts. Cook until it becomes caramel colored ( 298-300~ ). Turn into buttered 13 x 9 x 2 pan and allow to cool slightly then mark with a knife so you can cut it later. Let cool. Spread melted chocolate over cooled toffee. Sprinkle walnuts on top of chocolate. Let stand until set, then break into pieces and Eat. Makes 3 lb. Of toffee.