1. Beat egg yolks until they are thick and pale and gradually beat in sugar. Fold in whipped heavy cream and freeze the mixture until it is almost hard. Remove the cream from the freezer and let it soften slightly. Stir in the Cognac and dark rum, to taste. Stir in a few handfuls of rum-soaked raisins, if desired. Return the mixture to the freezer. Serve the eggnog in small punch cups, with spoons.