Stir the corn masa flour into the warm water. Let it sit for a couple minutes and strain it onto a saucepan set over medium heat. Incorporate the milk and let it simmer for 3 to 4 minutes, so it will begin to thicken. Incorporate the piloncillo or brown sugar, the chocolate and the cinnamon stick. Simmer for about 5 minutes, stirring here and there, until the chocolate and the piloncillo dissolve. Serve hot.