Departing from the satiny texture of a cream, a mousse is light and frothy. With a base of custard sauce, eggs (either whole or separated) beaten with sugar, or simply puréed fruit, a mousse acquires its volume from a generous amount of whipped cream and/or egg whites. Flavorings for a mousse must be forceful enough to cut through the richness of the cream and eggs; good choices are citrus fruits or tart berries—perhaps fortified with a splash of liqueur such as kirsch.
Cold soufflés are closely allied to mousses, the only difference being that soufflés are lightened with egg whites. Their preparation is a playful culinary illusion: to give the appearance of having risen in the oven like a hot soufflé, the mixture is set in the customary straight-sided soufflé mold fitted with a paper collar so that the mixture may be poured high above the rim of the mold.