In a medium saucepan over medium heat, whisk together egg yolks, milk, sugar, dark chocolate, cocoa powder, and cinnamon. When mixture is well combined and just starts to boil and bubble, remove from heat.
Pour mixture in a bowl over an ice bath and whisk for several minutes until cool. Whisk in cream, liqueur, and vanilla. Serve immediately or store in refrigerator.
Top with whipped cream and cinnamon if desired.
SNAPPY TIPS: Make sure you whisk the egg yolks and liquids well and slowly while over the heat so that the eggs don’t curdle.SNAPPY SUBSTITUTIONS: If you don’t like dark chocolate you could use original unsweetened cocoa powder, and substitute your favorite chopped chocolate for the chopped dark chocolate. You can also substitute any liqueur (such as rum or Baileys) for the chocolate liqueur or omit for a mocktail or kid version. EGG WHITES: Some people like to whip the egg whites (omitted from this recipe) and fold them into the finished drink. If you are concerned about raw eggs you may want to use pasteurized eggs or heat the whites first.DAIRY-FREE EGGNOG: For a dairy-free eggnog you can try substituting your favorite dairy-free chocolate and milk substitutes.