1. Stir together sugar, cocoa and salt in medium saucepan; stir in water. Cook over medium heat, stirring constantly, until mixture comes to a boil. Boil and stir 2 minutes. Add milk; stirring constantly, heat to serving temperature. Do Not Boil.
2. Remove from heat; add vanilla. Beat with rotary beater or whisk until foamy. Serve topped with marshmallows or whipped cream, if desired. Five 8-oz. servings.