custard

Custard is a variety of culinary preparations based on milk or cream cooked with egg yolk to thicken it, and sometimes also flour, corn starch, or gelatin. Depending on the recipe, custard may vary in consistency from a thin pouring sauce (crème anglaise) to the thick pastry cream (crème pâtissière) used to fill éclairs. The most common custards are used in desserts or dessert sauces and typically include sugar and vanilla, however savory custards are also found, e.g. in quiche.
Custard is usually cooked in a double boiler (bain-marie), or heated very gently in a saucepan on a stove, though custard can also be steamed, baked in the oven with or without a water bath, or even cooked in a pressure cooker. Custard preparation is a delicate operation, because a temperature increase of 3–6 °C (5–10 °F) leads to overcooking and curdling. Generally, a fully cooked custard should not exceed 80 °C (~175 °F); it begins setting at 70 °C (~160 °F). A water bath slows heat transfer and makes it easier to remove the custard from the oven before it curdles. Adding a small amount of cornflour to the egg-sugar mixture stabilises the resulting custard, allowing it to be cooked in a single pan as well as in a double-boiler. A sous-vide water bath may be used to precisely control temperature.

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