Whisk the masa harina with 1½ cups of the water until smooth and set aside.

Combine the remaining 6½ cups water, piloncillo and cinnamon stick in a large saucepan. Bring to a gentle simmer, stirring until the sugar dissolves.

Add the Mexican chocolate and whisk until melted. Stir in the whole milk and evaporated milk and heat gently.

Whisk the masa mixture again, then slowly pour it into the pot while whisking constantly. Simmer over low heat for 15–20 minutes, stirring often, until smooth and lightly thickened. Do not let the milk boil over.

Remove the cinnamon stick. Stir in the vanilla and salt. Taste and adjust sweetness if needed. Serve hot in mugs.