Step 1

Combine the milk and the cream in a 1-quart saucepan on medium heat. While the milk and cream are heating, combine the egg yolk, sugar, and nutmeg in a small bowl.

Step 2

When the milk mixture begins to simmer, remove from the heat and whisk 1 tablespoon of the milk mixture into the egg/sugar mixture. Continue to add and whisk 1 tablespoon at a time of the milk mixture to the egg mixture until you have added about half of the milk mixture to the egg.What you are doing here is tempering the egg. If you add the egg into the milk/cream mixture right away, the egg would cook and we don't want curdles in the eggnog. By tempering, you are slowly heating the egg to match the temperature of the milk.

Step 3

Pour the egg mixture into the saucepan. Return the pan back to the stove and reduce the heat to low. Stir or whisk constantly for about 10 minutes or until the mixture reaches the temperature of 160 degrees F. If you don't have a thermometer, cook the eggnog until it begins to thicken slightly, and coats the back of a spoon.Do not allow the mixture to boil, or it will curdle.

Step 4

Remove the saucepan from the heat and stir in the vanilla.

Step 5

Pour into a mug, add whisky, rum, bourbon, or brandy to taste, if desired. Refrigerate for at least 30 minutes.