Heat the milk, heavy cream, cinnamon sticks, vanilla, and nutmeg in a large saucepan over medium-high heat until it comes to a light boil, stirring occasionally.
In a medium bowl, add the eggs and beat on high speed while slowly adding the sugar. Beat on high speed until pale and fluffy. (about 2-3 minutes)
Whisk the egg mixture into the milk slowly. Heat over low until temperature reaches 160 degrees F.
Pour the eggnog through a fine sieve to make sure there are no scrambled egg pieces.
Pour into a large mug and top with whipped cream if desired, and a pinch of nutmeg.
Notes
Can be served hot or cold.
If using pasteurized eggs, there's no need to heat until 160 degrees.