Step 1In a medium saucepan, mix the cocoa powder, sugar, salt and water. Stir over medium-high heat, dissolving any lumps. Bring to a boil, then immediately lower the heat and simmer for 1 minute, stirring constantly.
Step 2Stir in the milk and half-and-half, and continue to cook until just heated through. Remove from the heat and add vanilla, if using. Serve immediately.