Makes about 6 cups
6 eggs, separated*
1 cup confectioner’s sugar, divided
2 teaspoons vanilla extract
1 large pinch cinnamon
½ teaspoon freshly grated nutmeg, plus more for garnish
Dark spiced rum, for serving
Brandy, for serving
Hot water, for serving
Separate the egg whites into the bowl of a stand mixer and the yolks into a separate clean, dry mixing bowl, making sure there is no yolk in the whites. Use the whisk attachment to whip the egg whites. After they begin to thicken, add half of the confectioner’s sugar (half cup), a spoonful at a time. Continue whipping until very stiff peaks form (this can take as long as 10 minutes, depending on your mixer).
To the bowl with the egg yolks, add the remaining confectioner’s sugar, vanilla, cinnamon, and nutmeg. Whisk to combine well. Add the yolk mixture to the whipped egg white mixture and fold very gently to combine.
Spoon a generous amount of the cocktail batter into each mug, about three tablespoons. Add a one-to-one ratio of rum and brandy. Pour piping hot water over the top until the mug is full. The batter will rise to the top as liquid is added. Garnish with freshly grated nutmeg and serve.
*Consuming raw or undercooked meats, poultry, seafood, shellfish, or eggs, may increase your risk of foodborne illness, especially if you have certain medical conditions.