Prepare the Egg MixtureIn a medium-sized bowl, whisk the egg yolks and sugar together until the mixture becomes pale and creamy. This ensures a smooth, velvety texture for your eggnog.
Heat the Milk and CreamIn a saucepan, combine the milk, heavy cream, cinnamon, and nutmeg. Heat the mixture over medium heat, stirring occasionally, until it’s hot but not boiling.
Temper the EggsSlowly add a small amount of the hot milk mixture to the egg mixture, whisking constantly to temper the eggs. Gradually whisk the tempered egg mixture back into the saucepan with the remaining milk and cream.
Cook and ThickenHeat the mixture over low-medium heat, stirring constantly, until it thickens slightly and coats the back of a spoon. Do not let it boil to prevent curdling.
Add Vanilla and ChillRemove the saucepan from the heat and stir in the vanilla extract. Allow the eggnog to cool to room temperature, then refrigerate for at least 2 hours before serving.
Serve and GarnishPour the chilled eggnog into glasses, top with whipped cream (if desired), and garnish with a sprinkle of nutmeg or cinnamon.