Serves 6 to 12
This can be made up to 3 days ahead and refrigerated, but if you use the spices, keep in mind their flavor intensifies over time.
Heat the milk in a medium saucepan over medium heat until it is hot to the touch. Whisk in the chocolate and sugar and continue whisking for 1 to 2 minutes until the sugar has dissolved. Whisk in the vanilla and the cinnamon and cayenne, if using. Reduce the heat to low. The chocolate may be made ahead; it will thicken as it sits.
Serve in demitasse cups or mugs depending on desired portion.
Note: For foamy hot chocolate, mix with an immersion blender just before serving. Or make hot chocolate ahead and reheat and froth it with the steam wand of an espresso machine. Or, top individual servings with frothed milk.