To make cornstarch slurry, combine equal amounts of cornstarch and cold liquid, such as water, broth or wine, and stir until it becomes a smooth paste. To thicken sauces or gravies, use 1 tablespoon of cornstarch for every cup of cooking liquid to be thickened.
Always use cold liquid to make the slurry, as boiling liquid added directly to cornstarch causes it to clump. Whisk the slurry into hot, simmering liquid, bring it to a boil and reduce it to simmering again, cooking until the liquid thickens. Avoid over-stirring and overheating, as the starch will break down and the liquid will thin out again.