Thickening with Cornstarch

" Cornstarch is a great thickener. Whether it's heated with a 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 bubbly. 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 the spoon."