Begin by pouring the homemade eggnog into a medium-sized saucepan. Place the saucepan over medium heat and gently warm the eggnog, being careful not to let it come to a boil.
While the eggnog is warming, take a separate mixing bowl and add the whole milk, freshly whipped cream, pure vanilla extract, and ground nutmeg. Whisk these ingredients together vigorously until they are well combined.
Once the eggnog is warm, slowly introduce it to the milk mixture by pouring it in gradually. Stir gently as you combine the two mixtures.
Return the combined mixture to the saucepan and heat it over low heat for a few more minutes. Stir frequently to maintain an even temperature.
After a few minutes, when the drink is warmed through and aromatic, turn off the heat. Carefully pour the creamy mixture into festive mugs.
To finish, sprinkle each mug with a touch of extra ground nutmeg, add a cinnamon stick to each mug, and garnish with dark chocolate shavings.