Heat the eggnog in a small saucepan until it barely comes to a simmer. Add the brandy and rum and pour into a mug. Top with the whipped cream and sprinkle with nutmeg.

To make your own eggnog, first whisk together the egg yolks with the sugar until well combined.

Heat the half and half and nutmeg in a saucepan until it comes to a simmer. Add a ladle of the hot liquid to the egg yolks while whisking. Add another ladle, whisking again, and a third, still whisking. Add the yolk mixture to the pan, whisking or stirring constantly over medium heat until it starts to thicken. (Don't let it boil.)