Begin by whisking the egg yolks and sugar in a medium bowl until the mixture becomes light and creamy.
In a saucepan set over medium-high heat, combine the heavy cream, milk, nutmeg, and salt. Stir frequently and heat until the mixture just begins to simmer.
Gradually add a spoonful of the hot milk to the egg mixture, whisking thoroughly after each addition. Continue this process until the egg mixture has been tempered.
Once most of the hot milk has been incorporated, return the combined mixture to the saucepan.
Stir the mixture continuously for approximately one minute, until it slightly thickens or reaches a temperature of 160°F. The eggnog will thicken further as it cools.
Remove the saucepan from the heat and stir in the vanilla extract and alcohol (if using).
Strain the eggnog through a fine mesh sieve into a pitcher or another suitable container. Cover with plastic wrap to prevent a skin from forming.
Refrigerate the eggnog until thoroughly chilled. It will naturally thicken as it cools. For a smoother, thinner texture, blend the eggnog with a couple of tablespoons of milk until desired consistency is achieved.
Before serving, garnish the eggnog with a sprinkle of cinnamon or nutmeg, and add fresh whipped cream if desired.
Store the homemade eggnog in the refrigerator for up to one week, ensuring it remains fresh for several days.
