In a stand mixer with the whisk attachment, beat the egg yolks until thick and pale yellow. Gradually add the sugar to the yolks. Beat in the milk and 2 ½ cups of the cream. Add the bourbon, rum, and cognac, stirring constantly. Refrigerate until ready to serve.

Just before serving, beat the egg whites until they are stiff, then fold them into the eggnog. Whip the remaining heavy cream until stiff peaks form, and it fold in. Sprinkle with nutmeg.