1. Place the reserved egg whites in a very clean and airtight container and freeze until the eggnog is ready to serve.
2. Combine the yolks and sugar in a large bowl and whisk until well blended and creamy.
3. Add the the remaining ingredients and stir to combine.
4. Transfer the mixture to a 1-gallon glass jar and tightly seal the lid. (Alternatively, you can bottle it.) Place in the refrigerator for at least 1 week and up to 3 weeks.

To serve:

1. The night before serving, place the frozen egg whites in the refrigerator to thaw.
2. When ready to serve, let the egg whites come to room temperature. Place the egg whites in the very clean bowl of a stand mixer fitted with a whisk attachment. Whisk on high speed until stiff peaks form, about 2 to 3 minutes. Remove to a large punch bowl.
3. Place the cream in the stand mixer bowl (no need to wash the bowl) and whisk on high speed until medium peaks form, about 1 to 2 minutes. Remove to the punch bowl.
4. Stir the eggnog base with a rubber spatula to re-combine, then add it to the punch bowl.
5. Gently whisk the eggnog together until just combined and no large pockets of whites or cream remain (do not overwhisk or you’ll deflate the eggnog).
6. Serve in punch cups over ice, if desired, and garnished with grated nutmeg.