This is the simplest possible dessert, and yet a great success. Make it in 5-ounce plastic cups for a large group. It can be made 2 or 3 days ahead, if you cover the containers to prevent “freezer smell.”
Beat the egg yolks and sugar together until stiff and lemon colored, then fold in the beaten egg whites and whipped cream and gently stir in the rum. Put into cups or a large bowl and freeze for at least 8 hours.