Take 4 eggs and separate the egg yolks from the whites. An idea is to save the whites later for little meringues
Heat 3 cups of milk in a saucepan on low-to-medium heat just until it begins to steam. Dont let it scald, so stir frequently
While you're waiting for milk to steam, put ice + a small amount of water in a large bowl. This will be used to cool down the egg nog once it has been cooked. You will place a smaller bowl on top of the ice water to give it an ice bath, but you dont want to get the water/ice into the mixture.
In a small - medium bowl whisk together the sugar and the egg yolks and egg until yellow and creamy.
Next step is to temper the eggs/milk so after the milk has steamed, take some of the hot milk and slowly pour into the yolk/sugar mix - whisking constantly. Do this until you've used about half of the warm milk, and then pour the entire mixture back into the saucepan
Keep the mixture warm over medium/low heat for about 20 mins. You want to whisk constantly to avoid scalding the milk and scrambling the eggs.
Once this has thickened slightly pour it into smaller bowl and place in bowl of ice. (note it doesnt really get as thick as traditional store-bought egg nog. These use xanthum gum as a thickener if you want to try it, but I have not)
Let this rest for about 20 mins to cool and then place in fridge for about 2 hours
Pour into small cups and grate fresh nutmeg on the top