Mix The Sugar And Flour In A heavy saucepan, blend in the water and heat, stirring constantly, over moderate heat until boiling and thickened. Reduce the heat to low, add the chocolate and cook and stir until the chocolate melts. Beat in the butter and vanilla. Cool slightly, beating now and then. Serve warm. And here's something else you might try. Simply begin your favorite fudge recipe, but cook the syrup only to about 220F or 225F. Take it off the heat, cool maybe 10 minutes, then drop in the butter, add the vanilla and heat until satiny. You couldn't get a more authentic hot fudge sauce than this! Makes 1 1/4 Cups