Cornstarch is a go-to ingredient for thickening sauces and stews, and all you need to do is whisk it into the liquid. However, you must remember to turn down the heat.

Boiling cornstarch for a minute or two makes its starch molecules big enough to absorb water, thickening the sauce, but further boiling can cause the starch to disintegrate.

Overcooking the cornstarch will thin out the sauce again, so stay on the safe side by turning the heat down to below a simmer as soon as the sauce starts to boil.

By turning down the heat before you add the cornstarch, it's less likely to disintegrate. Your pan will likely take a minute to cool, so there should be enough time for thickening.

Also, once you turn the heat down, avoid stirring the sauce. You'll interfere with the starch molecules as they absorb water, and this may prevent your sauce from thickening.

Another option is to add cornstarch towards the end of cooking your dish. This way, you can pull it off the stovetop if necessary to stop it from boiling too much.