In a medium bowl, whisk together the egg yolks and sugar until pale and slightly thickened.

In a saucepan, combine the heavy cream, whole milk, cinnamon stick, and cloves. Heat over medium heat until steaming, but do not boil.

Gradually pour a small amount of the hot cream mixture into the egg yolk mixture, whisking constantly to prevent the eggs from curdling. Repeat.

Pour the tempered egg mixture back into the saucepan with the remaining cream. Cook over low heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon (around 170-175°F or 77-79°C).

Immediately strain the eggnog through a fine-mesh sieve into a clean bowl.

Stir in the nutmeg, vanilla extract, and bourbon (if using).

Cover and refrigerate for at least 4 hours, or preferably overnight.

Before serving, whisk to recombine as settling is natural. Garnish with a sprinkle of freshly grated nutmeg. Serve chilled.