In a medium bowl, whisk the egg yolks and sugar together until light and creamy.
In a saucepan over medium-high heat, combine the heavy cream, milk, nutmeg and salt. Stir often until the mixture just reaches a simmer. Slowly carefully pour the hot milk to the egg mixture, whisking constantly until just combined.
Bring the entire mixture back to the saucepan over medium high heat. Continue cooking and whisking for just another minute or two until it slightly thickens, or when the mixture reaches 160-165°F(71-74°C) on an instant-read digital thermometer. The mixture will continue to thicken more as it cools.
Remove from heat and stir in the vanilla, and alcohol*, if using. Pour the eggnog through a fine mesh strainer into a container and cover with a lid or a plastic wrap. Refrigerate until chilled.
Serve the eggnog with whipped cream and a dash of ground cinnamon or nutmeg, if desired. Store homemade eggnog in the fridge for up to one week.