In medium saucepan, combine sugar, cocoa and salt; blend in water. Cook over medium heat, stirring constantly, until mixture boils. Boil and stir 2 minutes. Add milk; stir and heat to serving temperature. DO NOT BOIL. Remove from heat; add vanilla. Beat with rotary beater or wire whisk until foamy. Serve hot, topped with sweetened whipped cream, if desired.
In microwave proof cup or mug, combine cocoa, sugar and salt. Add 2 teaspoons cold milk; stir until smooth. Fill cup with milk; microwave on high 1–1½ minutes, or until hot. Stir to blend; serve.