Separate the eggs and store the whites for another application.
In a small bowl, mix the sugar and nutmeg (and cocoa if making chocolate eggnog).
With a hand mixer, gently beat the yolks until blended. While beating, slowly add the sugar mix until the mixture lightens in color and falls off the whisk in a solid ribbon.
Combine dairy, booze, and salt in a second bowl or pitcher and then slowly beat into the egg mixture.
Move to a large glass jar (or a couple of smaller ones) and store in the fridge for a minimum of 2 weeks. A month would be better, and 2 better still. And yes, you can also drink it right away.