How to Thicken Sauces with Cornstarch 

When added to liquid and heated, cornstarch’s granules absorb water and form a gel. It’s pretty powerful too: Usually just a teaspoon or so is enough to thicken a whole batch of sauce. But you have to be strategic about how you use it. If you add cornstarch straight into a sauce you’re cooking, it’ll clump relentlessly. Instead, you’ll want to use one of these approaches.

1. For quick-cooking sauces, you can mix cornstarch right into the sauce ingredients before you begin cooking (since cornstarch only clumps when heated). Add the sauce-cornstarch mixture to the pan and cook it all together for almost instant thickening, like we do for these Honey-Soy Steak Tips with Roasted Green Beans and Sweet-and-Sour Baby Back Ribs.
2. If you have a sauce already cooking that needs thickening, you’ll want to use a slurry: Mix the cornstarch into cold or room-temperature liquid (either water or another liquid ingredient in your sauce) to make a cloudy mixture called a slurry. You can then whisk this slurry into your skillet or pot for smooth, clump-free thickening, as we do in this Red Wine Sauce and Roast Pork Loin with Dried Fruit. 

Cornstarch usually requires only a minute or so of boiling to reach its full thickening potential; cook it too long, though, and your sauce will start to thin out again, so be careful!