About halfway through the red wine's mulling time, make the hot chocolate component. Place 12 ounces finely chopped chocolate in a large mason jar, and set aside. In a medium saucepan, combine 1 cup heavy cream and 1 cup whole milk. Place on medium-high heat and warm until just about ready to boil, and immediately remove from heat and pour over the chopped chocolate in the mason jar. Let sit for at least 5 to 10 minutes, before whisking to dissolve the chocolate completely. Seal the lid tightly on the mason jar, and give the mixture a good shake if that helps!