Use Flour
Flour can easily be used in a pinch. Keep in mind, however, that while cornstarch gives whatever it’s thickening a glossy shine, flour won’t—it will result in a final product that’s more matte.
For every 1 tablespoon of cornstarch, you’ll need to use about 3 tablespoons of flour. Also, cook whatever you’re thickening a few minutes longer to get rid of the raw flavor of the flour.
Use Arrowroot
Made from the root of the plant of the same name, this type of starch is an easy one-to-one substitution for cornstarch. It will also produce the same glossy finish that cornstarch does.
Use Potato Starch
Another one-to-one substitution—just be careful when you whisk, it tends to clump up more than cornstarch.
Use Tapioca Flour
Also know as tapioca starch, it’s a great substitute. You’ll want to use 2 tablespoons for every 1 tablespoon of cornstarch.
Use Rice Flour
Rice flour thickens up like regular flour so use the same proportion: 3 tablespoons for every 1 tablespoon of cornstarch