Fill a large wide bowl with ice and cold water, and set it aside.

In a medium bowl, whisk the egg yolks with 1 cup of the sugar until the mixture is pale yellow and thick, about 2 minutes.

Combine the milk, vanilla bean, and salt in a medium saucepan. Set it over medium heat and bring the mixture to a boil. Remove the pan from the heat.

While whisking constantly, slowly drizzle 1 cup of the hot milk into the yolks. Add 1 more cup of the hot milk to the yolks in the same manner.

Now that the yolks have been tempered, slowly pour the yolk mixture into the saucepan with the remaining milk while continuing to whisk. Cook over medium heat, stirring constantly with a wooden spoon, for 3 minutes, or until the mixture is thick enough to coat the back of the spoon. Remove the saucepan from the heat.

Pour the mixture through a fine-mesh strainer into a large metal bowl set in the ice bath. Stir as needed until cooled, about 20 minutes.

Cover the eggnog base, and refrigerate until it is well chilled and ready to use, at least 1 hour or up to overnight.

Place the egg whites (see Note 1) in the bowl of a standing electric mixer fitted with the whisk attachment, and beat until soft peaks form. Slowly add the remaining ¾ cup sugar, beating the whites on high speed until stiff peaks form.

Remove the chilled eggnog base from the refrigerator. Whisk in the bourbon, brandy, and rum. Whisk in the heavy cream (see Note 2).

Fold in the whipped egg whites, and whisk until the mixture is uniform. Serve immediately, with freshly grated nutmeg if desired, or refrigerate until ready to enjoy.

Notes:

1. If you prefer to make this eggnog without raw egg whites, eliminate step 5 from the recipe. Instead, whip 3 cups of cream (the 2 cups plus an additional cup) with the ¾ cup sugar until thick, and add this to the eggnog base in step 6. Discard the egg whites or reserve for another use.

2. If you prefer a thicker eggnog, whip the cream before adding it to the eggnog base.