In a large bowl, combine egg yolks, 1 cup sugar and rum. Mix well, cover and refrigerate overnight.
Stir the milk into the cooled yolk mixture. In a large bowl, whip the cream until soft peaks form; set aside.
In a separate clean bowl, with a clean whisk, whip egg whites until thick, then gradually add the 1/2 cup of white sugar and whip until peaks form. Fold the whipped cream into the egg whites, then fold into the yolks mixture. Pour into mugs and sprinkle top with nutmeg.