Definition of 'optimum'. optimum (ÉptÉªmÉm ) or optimal. The optimum or optimal level or state of something is the best level or state that it could achieve. Aim to do some physical activity three times a week for optimum health. ...regions in which optimal conditions for farming can be created.
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.
Though a home cook can't make cornstarch at home, it's possible to make a good substitute: potato starch. Use an equal amount of potato starch in recipes that call for cornstarch, including soups, sauces, gravies and custards. To make potato starch, grate potatoes into a bowl and add some warm water.