In a heavy 2 to 3 quart saucepan, combine the chocolate and milk. Cook over low heat, stirring constantly, until the chocolate has melted completely and the mixture is well blended and hot. Do not let the mixture come to a boil. With a molinillo (Mexican wooden beater) or a rotary beater, beat the chocolate vigorously until it is foamy. Pour it into individual cups and serve at once.