Working with Creams and Custards

Custards (derived from croustade, a flaky pastry case) date back to the Middle Ages, when they were used as fillings for flans or tarts. A custard is a mixture of liquid and egg that, when gently heated, thickens or sets by the coagulation of egg proteins. Custards may be sweet or savory; they may use whole eggs, whole eggs plus yolks, or yolks alone. They usually contain cream, milk, or both, but they may also be made with liquids other than milk, as in fruit curds and zabaione. The consistency of a finished custard is determined by the ratio of eggs to liquid. (One whole egg or 2 egg yolks will set 1 cup of milk into a loose custard. A firmer gel requires more protein, usually 3 whole eggs per 2 cups of milk.)