Hot Cocoa is versatile. You can make it as lean or rich as you like by choosing nonfat, low fat or whole milk. You can even make hot cocoa with water instead of milk, as though it were coffee, and then add cream and sugar to your taste!
In a small, heavy saucepan, mix the cocoa and sugar with about a tablespoon of the milk to make a smooth paste. Stir in the rest of the milk and cook over low heat, stirring frequently, until hot but not boiling. Serve immediately, or let cool and refrigerate: reheat before serving.