Combine the rolled oats, eggnog, milk, chia seeds, maple syrup, vanilla extract, nutmeg, and cinnamon in a jar or container with a lid.
Stir all ingredients thoroughly to ensure everything is well combined. Make sure there are no clumps of chia seeds at the bottom of the jar.
Cover the jar tightly and refrigerate for at least 4 hours, or preferably overnight.
Check the consistency of the oats. If they seem too thick, add a splash of milk to thin them out. If they’re too thin, add a teaspoon of chia seeds and let them sit for another 30 minutes.
Before serving, add your favorite toppings.
Enjoy your delicious and festive Eggnog Overnight Oats!