In a large bowl or the top part of a double boiler, beat egg yolks and sugar until pale and thick. Set bowl or top part of double boiler over simmering water, do not let water boil. Add Marsala, sherry or port slowly, beating constantly. Zabaglione is ready when mixture has tripled in volume and it is soft and fluffy, after 4 to 6 minutes. Spoon into individual glasses. Serve immediately.

Cold Zabaglione (Zabaglione Freddo):

As soon as Zabaglione swells up into a soft mass, set bowl or top part of double boiler over a bowl of ice water. Continue stirring until cool. Spoon into glasses and refrigerate until ready to serve.