Whisk the egg yolks and sugar together in a medium bowl until pale yellow and creamy.
In a saucepan over medium-high heat, combine the cream, milk, nutmeg, cinnamon and salt. Stir the mixture until it reaches a simmer.
Temper the eggs by slowly adding half of the hot milk mixture into the eggs, whisking constantly while you add the milk. Pour the mixture back into the saucepan.
Cook the eggnog on medium heat, stirring constantly with a wooden spoon, until the mixture begins to thicken slightly, and coats the back of the spoon. If you have a candy thermometer, cook until the mixture reaches 160°F.
Remove from heat and stir in the vanilla extract. Pour the eggnog into a pitcher or container and cover with plastic wrap. Refrigerate until chilled as it will thicken as it cools. You can keep in the fridge for 2-3 days.
Use fresh, quality eggs.
Adjust the sugar to your liking. Add more or less.
If you really love nutmeg, you can add ¼ teaspoon at a time till it is to your liking.
Want your eggnog creamier? Use more cream and less milk. Or stir in some whipped cream.