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A bowl of crème anglaise custard, dusted with nutmeg
Custard is a variety of culinary preparations based on a cooked mixture of milk or cream and egg yolk. Depending on how much egg or thickener is used, custard may vary in consistency from a thin pouring sauce (crème anglaise) to a thick pastry cream (crème pâtissière) used to fill éclairs. Most common custards are used as desserts or dessert sauces and typically include sugar and vanilla. Custard bases may also be used for quiches and other savoury foods. Sometimes flour, corn starch, or gelatine is added as in pastry cream or crème pâtissière.
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 (176 °F); it begins setting at 70 °C (158 °F). A water bath slows heat transfer and makes it easier to remove the custard from the oven before it curdles.
A bowl of custard with a teaspoon
Mixtures of milk and eggs thickened by heat have long been part of French cuisine. Custards baked in pastry (custard tarts) were very popular in the Middle Ages, and are the origin of the English word 'custard': the French term 'croustade' originally referred to the crust of a tart, and is derived from the Italian word crostata, and ultimately the Latin crustāre.
Examples include Crustardes of flessh and Crustade, in The Forme of Cury. These recipes include solid ingredients such as meat, fish, and fruit bound by the custard. Stirred custards cooked in pots are also found under the names Creme Boylede and Creme boiled.
In modern times, the name 'custard' is sometimes applied to starch-thickened preparations like blancmange and Bird's Custard.
A formal custard preparation, garnished with raspberries
While custard may refer to a wide variety of thickened dishes, technically (and in French cookery) the word "custard" (crème or more precisely crème moulée, [kʁɛm mule]) refers only to an egg-thickened custard.
When starch is added, the result is called pastry cream (French: crème pâtissière) or confectioners' custard, made with a combination of milk or cream, egg yolks, fine sugar, flour or some other starch, and usually a flavouring such as vanilla, chocolate, or lemon. Crème pâtissière is a key ingredient in many French desserts including mille-feuille (or Napoleons) and filled tarts. It is also used in Italian pastry and sometimes in Boston cream pie. Although egg thickens the custard, the effect is minimal, with the majority of thickening resulting from starch. Corn flour or flour thicken at 100 °C and as such many recipes instruct the pastry cream to be boiled. In a traditional custard such as a crème anglaise, where egg is used alone as a thickener, boiling results in the over cooking and subsequent 'curdling' of the custard; however, in a pastry cream, starch prevents this. Once cooled, the amount of starch in pastry cream 'sets' the cream and requires it to be beaten or whipped before use.
Layers of a trifle showing the custard in between cake, fruit & whipped cream
When gelatine is added, it is known as crème anglaise collée. When starch is used alone as a thickener (without eggs), the result is a blancmange. In the United Kingdom, custard has various traditional recipes some thickened principally with cornflour (cornstarch) rather than the egg component, others involving regular flour; see custard powder.
After the custard has thickened, it may be mixed with other ingredients: mixed with stiffly beaten egg whites and gelatine, it is chiboust cream; mixed with whipped cream, it is crème légère.
Savoury custard: Not all custards are sweet. A quiche is a savoury custard tart. Some kinds of timbale or vegetable loaf are made of a custard base mixed with chopped savoury ingredients. Custard royale is a thick custard cut into decorative shapes and used to garnish soup, stew or broth. In German it is known as Eierstich and is used as a garnish in German Wedding Soup (Hochzeitssuppe). Chawanmushi is a Japanese savoury custard, cooked and served in a small bowl or on a saucer.
Custard may also be used as a top layer in gratins, such as the South African bobotie and many Balkan versions of moussaka.
Recipes involving sweet custard are listed in the custard dessert category, and include:
Cooked (set) custard is a weak gel, viscous and thixotropic; while it does become easier to stir the more it is manipulated, it does not, unlike many other thixotropic liquids, recover its lost viscosity over time.
A suspension of uncooked imitation custard powder (starch) in water, with the proper proportions, has the opposite rheological property: it is negative thixotropic, or dilatant, allowing the demonstration of "walking on custard"; see the physical properties of custard powder.
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