Whisk the egg yolks and granulated sugar in a bowl until smooth and creamy.
Add to the Crockpot along with the remaining ingredients (except for the whipped cream).
Stir to combine.
Cover and cook on low for 1½ hours, stirring 1-2 times throughout the cooking process.
Remove the lid, give the eggnog another stir. Let the mixture cool for about 30 minutes.
Remove the cinnamon stick.
Transfer the eggnog to a beverage container and chill in the refrigerator until ready to serve. The mixture will thicken as it chills.
Serve in glasses with whipped cream and a dusting of ground nutmeg or cinnamon.