Custard is a variety of culinary preparations based on a cooked mixture of milk and/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 (French: 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 savory foods. Sometimes flour, corn starch, or gelatin is added as in pastry cream or crème pâtissière. (source)