As the materials used in the preparation of cocoa and chocolate are rather expensive, not the slightest quantity of these beverages that remains after serving should be wasted. However, a small amount of chocolate usually has to be added so that it will have a stronger flavor. It may then be thickened with corn starch for chocolate blanc mange or with gelatine for chocolate jelly. Either of these served with whipped cream or a sauce of some kind makes an excellent dessert. Chocolate bread pudding may also be flavored with these left-over beverages.
It is also a good plan to utilize left-over cocoa or chocolate for flavoring purposes. However, additional cocoa or chocolate and sugar should first be added to it, and the mixture should then be boiled to a sirup. When so prepared it may be used whenever a chocolate flavoring is desired, such as for flavoring other beverages, cake icings, custards, sauces for desserts, and ice creams.
Woman's Institute Library of Cookery, Volume 5.