Brew 2 cups of coffee at triple strength; set aside.
Measure 3 cups eggnog, 1 cup milk, 1/4 cup vanilla sugar (or regular granulated sugar), 1 teaspoon vanilla extract, and 1/4 teaspoon grated nutmeg; reserve any extra nutmeg for topping if desired.
Pour the brewed coffee, eggnog, milk, sugar, vanilla extract, and 1/4 teaspoon grated nutmeg into a 2.5‑quart (or larger) Crock Pot.
Stir well to combine and to help dissolve the sugar.
Cover and cook on Low for 2 hours, stirring occasionally, until the mixture is piping hot.
After it reaches piping hot, reduce the Crock Pot to the Warm setting to keep the lattes hot throughout the day.
Before serving, stir the mixture, ladle into mugs, and sprinkle additional grated nutmeg on top if desired.