Prepare your glass by dipping the edge into a small plate of water. Then dip the wet edge into the mount of spiced sugar. Set aside.
To a cocktail shaker add the Eggnog and Fireball.
Add ice and shake well.
Strain over fresh ice in a short cocktail glass.
Grate fresh nutmeg on top and drink immediately.
Notes
Be sure to mind the ratios, unless you don't care about getting the full eggnog flavor.
My sister-in-law was telling me about some holiday flavored liqueurs from Trader Joe's. They have an eggnog flavor. If you have it, add an ounce to this to enhance the eggnog flavor.
I'm sure you can use an eggnog alternative like those made with almond milk, but you will lose the creaminess. And I'm not sure how bold the flavors are. You may need to taste first and adjust the amount of Fireball as needed.
Fireball now makes their own premade Fireball Eggnog. Look for it in stores. I've heard that Walmart carries it. Its all made for you and you just need to pour it in a glass and enjoy. I have not tried it yet so I can't speak to the flavor.