MAKES 1 QT. BASE
With an electric mixer on low speed, whisk 12 large eggs with 18 ounces sugar until the sugar has dissolved. Pouring very slowly so as not to curdle the eggs, whisk in 1½ cups bourbon, ½ cup cognac, and ⅓ cup dark rum. Stir in a pinch each of salt and freshly ground nutmeg, then transfer to a sanitized glass jar and tightly seal. Refrigerate 3 weeks or up to 2 years, shaking the jar at least once a month. To serve, combine 2¾ ounces eggnog base, 1¼ ounces whole milk, and ¼ ounce heavy cream in a cocktail shaker with ice. Shake until frothy. Strain into a chilled coupe glass and top with freshly grated nutmeg.