In a medium-sized mixing bowl, combine the 6 egg yolks and the granulated sugar. Use a whisk or an electric hand mixer to beat them together until the mixture becomes pale yellow and slightly fluffy. This creates a smooth base for your holiday drink.

Place a heavy-bottomed saucepan over medium heat. Pour in the whole milk, heavy cream, ground nutmeg, cinnamon, and a pinch of salt. Stir the mixture occasionally to prevent a skin from forming. Heat the liquid until it starts to simmer and small bubbles appear around the edges, but do not let it reach a full, rolling boil.

To prevent the eggs from scrambling, you must temper them. Slowly pour a half-cup of the hot milk mixture into the egg yolk bowl while whisking constantly. Once incorporated, add another half-cup and continue whisking. This gradually raises the temperature of the yolks so they stay smooth and creamy.

Pour the tempered egg mixture back into the saucepan with the remaining hot milk. Set the heat to low and cook the mixture for about 3 to 5 minutes. Stir constantly with a wooden spoon until the liquid thickens enough to coat the back of the spoon. Remove the pan from the heat and stir in the vanilla extract (and the alcohol if you are making the boozy version).

Pour the eggnog into a pitcher and cover it with plastic wrap, ensuring the wrap touches the surface of the liquid to prevent a film. Refrigerate for at least 3 hours or overnight. When ready to serve, pour into glasses and top with whipped cream and a sprinkle of extra nutmeg.