Beat yolks until light. Add sugar and mix well. Add milk and rum. Mix well, then chill for at least 3 hours. One hour before serving, whip cream and stir into chilled mixture. Return to refrigerator for an hour. Serve in punch cups and dust with nutmeg.
NOTE: This stuff is POTENT, even if you reduce the rum by half. brandy, dark rum or bourbon may be substituted for the light rum. If you prefer a nonalcoholic eggnog, leave out the alcohol altogether. With or without alcohol, this eggnog is very rich and very good.