Preparation

1. In large bowl, beat egg yolks, vanilla extract, and sugar together until mixture is smooth and no longer grainy.
2. Stir in milk, whipping cream, and rum (if using), then pour mixture into slow cooker.
3. Cook on low for 2 hours, whisking every 20 to 30 minutes to prevent boiling. Once eggnog coats the back of a spoon, it's done.
4. Serve eggnog warm in mugs garnished with cinnamon stick and sprinkled with ground cinnamon.