Custard powder is predominantly made of a starch, such as tapioca or cornstarch, along with flavoring such as vanilla, salt and annatto for color. The powder is colored and flavored so that it gains the look and flavor of custard once it is mixed with hot milk.
Custard powder is predominantly used in Britain as an alternative to using eggs for making custard. It was invented in the 1830s by Alfred Bird, whose wife enjoyed custard but was allergic to eggs. He named the product Bird's, which remains a widely used brand in the United Kingdom. Use custard powder to make custard by mixing it with boiling milk or cream and sugar to taste. Use it to make a custard sauce by mixing it with hot milk and seasonings such as herbs and spices as desired.
Custard powder is different than instant custard, which is typically prepared by adding water. Instant custard contains more ingredients than custard powder, including sugar, milk proteins, oil and cream powder. Because it is a specialized product, custard powder may be difficult to locate. Substitute it with vanilla instant pudding, or mix up a custard powder substitute by combining three parts cornstarch with one part vanilla extract and a pinch of salt.