Add the milk and heavy cream to a medium saucepan.

Warm the mixture over medium heat until steaming but not boiling.

Place the egg yolks and sugar into a mixing bowl.

Whisk the yolks and sugar until the mixture becomes pale and slightly thickened.

Slowly ladle a small amount of the warm milk mixture into the yolk mixture.

Whisk constantly to temper the eggs.

Continue adding warm milk to the yolks in small amounts while whisking.

Pour the tempered yolk mixture back into the saucepan.

Cook the mixture over medium heat while stirring continuously.

Heat until the mixture lightly coats the back of a spoon.

Remove the saucepan from the heat.

Stir in the vanilla extract, ground nutmeg, ground cinnamon, and salt.

Add the optional bourbon, rum, or brandy if using.

Pour the eggnog through a fine mesh strainer into a large container or pitcher.

Cool the eggnog to room temperature.

Cover the container and refrigerate until fully chilled.

Serve cold with a sprinkle of nutmeg on top.