Step 1: Heat milk and cream on medium heat until steaming. Whisk occasionally.
Step 2: Whisk egg yolks and sugar in a separate bowl. Carefully add in ⅓ of the warm milk mixture into the egg yolk combination to temper the eggs. Be sure to keep mixing.
Step 3: Transfer the milk & yolk mixture into the pot on the stove, and cook until thickened (about 5 minutes, or until mixture reaches 165°). Whisk continuously. At this point, you can add in alcohol for a spiked eggnog drink, OR wait until the very last step to beat in alcohol.
Step 4: Strain eggnog through a fine-mesh strainer and whisk in vanilla and nutmeg. Refrigerate eggnog for at least two hours.
Step 5: If you did not add in alcohol in step 3, you can beat it now on medium speed. Otherwise, pour into glasses, add some PICS whipped cream, and enjoy!