In a medium saucepan, combine the milk, cinnamon, cloves, and ½ teaspoon of vanilla extract. Warm over low heat for 5 minutes, stirring occasionally. Gradually increase the heat to medium-low and bring the mixture to a gentle boil. Remove from heat and let it cool slightly.

In a large mixing bowl, whisk the egg yolks until they are pale and creamy. Gradually add the sugar and continue whisking until the mixture becomes light and fluffy. This step ensures a smooth texture for your eggnog.

Slowly pour a small amount of the warm milk mixture into the egg yolk mixture while whisking constantly. Gradually add the remaining milk mixture in a steady stream, continuing to whisk. This process gently heats the eggs without curdling them.

Pour the tempered mixture back into the saucepan. Cook over medium heat, stirring constantly, until the mixture thickens slightly and coats the back of a spoon, about 3 minutes. Do not let it boil, as this can cause the mixture to curdle.

Strain the mixture through a fine-mesh sieve to remove the cloves and any cooked egg particles. Allow the mixture to cool at room temperature for 1 hour.

Once cooled, stir in the cream, remaining 2 teaspoons of vanilla extract, rum (if using), and nutmeg. Mix thoroughly to combine.

Transfer the eggnog to a pitcher or airtight container and refrigerate for at least 8 hours, or overnight. Serve chilled, garnished with an extra sprinkle of nutmeg or a cinnamon stick for decoration.