How to Thicken with Cornstarch

Learn our correctly thicken custard with cornstarch.

Cornstarch is a great thickener. Whether it's heated with the liquid it's to thicken, or is added into a hot liquid, the general rule of thumb is to use 1 tablespoon of cornstarch for each cup of liquid. Here, to make custard, cornstarch and sugar are whisked together. Then, the milk is added. The mixture is cooked over medium heat, whisking to keep it smooth until thickened and bubbling. If the cornstarch were to be added into a hot liquid, for example a stir fry sauce, it would first be mixed with water, added to the hot liquid, and whisked until the proper consistency. It is properly thickened when it coats the back of a spoon.