Toast masa harina in pan over low heat; cool.

In an olla or other large, heavy-bottomed pot, over medium heat, stir piloncillo, cinnamon, chocolate, and water until they dissolve.

Put cooled masa harina in a blender with milk, then add to hot water mixture. Cook over medium-high heat until it boils, whisking constantly, then lower heat and continue whisking until it reaches a desired thicker consistency. Remove from heat.