Beat Eggs: Crack 4 large eggs and separate the whites from the yolks. In a mixing bowl, beat the egg yolks only until they are smooth.
Add Sugar: Gradually add ½ cup sugar to the egg yolks while continuing to whisk.
Beat Egg Whites (optional): Whisk the egg whites until frothy. Once it is done, sprinkle three pinches of sugar into the egg white.
Prep Milk Base: In a saucepan, combine 2 cups whole milk, 1 cup heavy cream, and 2 cinnamon sticks. Gratte about ⅓ Nutmeg and add it to the mix.
Heat Milk: Heat the milk mixture in a saucepan until it's just about to boil.
Combine Mixtures: With the heating off, slowly pour the egg yolk mixture into the hot milk, whisking constantly.
Cook: Switch again the heating on and cook over medium heat, stirring constantly until it thickens slightly.
Add Bourbon: Remove from heat and let it cool down for a bit. Then, add ¾ cup bourbon and 3 drops vanilla extract.
Combine Mixtures: Carefully combine the foamy egg whites with the eggnog mixture.
Serve: Pour into serving glasses and sprinkle with nutmeg if desired.