Arrowroot and cornstarch have similar thickening capabilities. Generally, add 2-3 teaspoons to a cup of liquid for a medium-thick sauce. Arrowroot gives a little higher gloss to sauces than cornstarch, which is more desirable than the cloudy look that comes from a sauce thickened with flour. Like cornstarch, arrowroot is flavorless, so it should be acceptable to the entire family.
Arrowroot is not recommended as a replacement for cornstarch in dairy-based sauces because it becomes slimy when mixed with milk.
If you plan to use arrowroot in place of cornstarch in other recipes, keep a few additional things in mind. Arrowroot thickens better than cornstarch in an acidic liquid, such as a citrus sauce for a dessert. So be sure to start with a little less arrowroot than the amount of cornstarch called for in a recipe.
Arrowroot can also be used to thicken gravy, but the gravy will not hold well, nor will it reheat well. So you should prepare arrowroot gravy no more than 10 minutes prior to serving. Or use flour as the thickening agent.
To replace cornstarch with flour, use twice as much all-purpose flour. Mix the flour with some of the liquid in the recipe to make a slurry before heating.