1. Combine first 5 ingredients in a medium saucepan. Bring to a boil over medium heat, stirring constantly with a whisk. Place egg yolks in a medium bowl. Gradually whisk one-third of hot milk mixture into egg yolks. Add yolk mixture to remaining hot milk mixture, stirring with a whisk. Cook over medium heat 1 minute or until slightly thickened. Pour into a pitcher; stir in bourbon, brandy, and vanilla.
2. Cover surface of eggnog with wax paper; refrigerate at least 4 hours or overnight. Garnish with additional nutmeg, if desired.