In a heavy pot, whisk together the milk and cornstarch.
Once the cornstarch is dissolved, heat the milk mixture over medium-low heat just until it starts to simmer, then remove from heat.
Add the chopped chocolate and immediately and begin stirring until the chocolate is completely melted. If the milk cools off too fast, place the pan back on the stove on low heat to melt the chocolate. At this point, taste the hot chocolate and add sugar if desired.
The mixture should thicken quickly. As soon as you see it thicken, remove the pan from the heat so the cornstarch will not thin.
Ladle immediately into small cups or bowls and serve piping hot.
Yields 2 cups.
Hot Chocolate Sauce - Spanish Chocolate Caliente Recipe: https://whatscookingamerica.net/spain-trip-2014/spanish-chocolate-caliente.htm