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

Heat the milk mixture. In a medium saucepan, combine the milk, cream, cinnamon, nutmeg, and salt. Warm over medium heat until steaming (don’t let it boil).

Temper the eggs. Slowly whisk about ½ cup of the hot milk mixture into the yolks to warm them. Gradually add the rest of the hot milk mixture, whisking constantly.

Cook to thicken. Return everything to the saucepan and cook over medium-low heat, stirring constantly, until the mixture reaches 160–165°F and lightly coats the back of a spoon.

Finish. Remove from the heat, stir in the vanilla and liquor (if using).

Chill + serve. Transfer to a pitcher, cover, and chill at least 2–3 hours before serving. Garnish with a dusting of nutmeg.