Crack and separate 12 large eggs, placing yolks in one large bowl and whites in another.

Whisk the egg yolks with 1/2 cup of the granulated sugar in a bowl until pale and ribbony, about 3 minutes.

Combine 2 cups whole milk and 2 cups heavy cream in a large heavy-bottomed saucepan and warm over medium heat until the mixture reaches 160°F, about 7-8 minutes, without boiling.

Remove the saucepan from heat and slowly ladle half of the warm milk mixture into the yolk mixture while whisking constantly to temper the eggs.

Pour the tempered yolk mixture back into the saucepan with the remaining milk and cream and return to medium heat.

Stir constantly with a wooden spoon and cook until the custard reaches 160°F, about 3-4 minutes.

Strain the custard through a fine mesh strainer into a large bowl, then cover and refrigerate for at least 1 hour or until completely cold.

With an electric mixer, beat the egg whites and remaining 1/4 cup sugar until soft peaks form.

Stir 1 cup bourbon whiskey, 1/4 cup dark rum, 2 teaspoons vanilla extract, 1/2 teaspoon freshly grated nutmeg, 1/4 teaspoon ground cinnamon, and a pinch of sea salt into the cold custard base.

Gently fold the whipped egg whites into the custard mixture in two batches until just combined.

Transfer the eggnog to a glass pitcher or serving bowl and refrigerate until ready to serve, at least 1 hour.