Fill a cambro or large pot with enough water to cover the jar(s) that you'll be making your eggnog in. Using your sous vide/immersion circulator, preheat the water to 144° F.
While the water preheats, add the egg yolks and sugar to a blender. Blend until the yolks are lighter in color and a bit fluffier.
Add the milk, cream, vanilla, nutmeg, and salt to the blender. Blend until everything is well incorporated. If you're adding the *optional* alcohol to this recipe, add it here and blend it well.
Add the cinnamon stick to the jar, followed by the contents of the blender.
Place the lids on the jars to finger tight. That is, tighten the lids well, then unscrew them approximately half a turn.
Carefully place the jar into the preheated water and cook for 1 hour.
Remove the jar from the water and allow it to cool a bit before storing it in the fridge for at least 4 hours. It will thicken more as it chills.
When you're ready to drink the eggnog, remove the cinnamon stick from the jar and pour it into a glass. Garnish with some whipped cream and a little freshly grated nutmeg.