Heat together 1/2 cup of milk and 1/2 cup of eggnog for about 1 minute in the microwave. Froth mixture using a milk frother. The milk will froth up and almost double in size.
If you don't have a frother, you can pour the heated milk and eggnog mixture into a blender for about 30 seconds.
If you don't have a blender, you can put the heated milk and eggnog mixture in a jar or cocktail shaker and shake for about 1 minute.
Pour espresso or coffee into a coffee cup, and top with 1/2 of the milk and eggnog.
Top with whipped cream and grated nutmeg if desired.