In a small saucepan, whisk together the ¾ cup of the milk, the cream and sugar. Set the saucepan over medium-low heat and cook until it starts to bubble around the edges.
While the milk mixture is heating, whisk together the remaining ¼ milk and the cornstarch until it is smooth. Once the milk mixture starts bubbling around the edges, add the milk and cornstarch mixture and whisk until it’s heated through, about 1 minute.
Add the the chopped chocolate and whisk together until it’s smooth and thick enough to coat a spoon, about 5 minutes. Remove from the heat, pour into mugs and serve with whipped cream if desired (this recipe filled two standard coffee mugs for me, but it's pretty rich, so I could definitely see only having a half cupful if you prefer). The drink will continue to thicken if it is left to sit off the heat.
Note: To spike these drinks, whisk 1½ tablespoons of your favorite liqueur into the hot chocolate after removing from the heat.Nutritional vales are based on one serving