Measure

• Ounce for ounce, cornstarch has more thickening power than flour. For this reason, when substituting flour for cornstarch in your pie filling, you need to double the amount of flour tablespoon for tablespoon. For example, a classic blueberry pie recipe in The Joy of Cooking online calls for 2 tablespoons of cornstarch. When using flour, you double this amount and use 4 tablespoons instead.

Combine

• Cornstarch imparts a neutral flavor even without adding heat, but flour needs to be cooked, preferably with a fat of some kind, to remove its somewhat unappealing raw taste. When baking your filling in a pie, the flour blends with the fruit’s naturally released juices, to thicken your filling. If not already called for in the recipe, adding a little fat helps improve the taste of your flour-made filling. To do this, simply dot the filling -- before covering with the crust -- with 1 to 2 tablespoons of butter, cut into small pieces.

Cover

• Cornstarch is praised for the glossy sheen it gives to fillings in baked goods. Flour, on the other hand, results in an opaque filling, which many consider less attractive. If appearance is a concern, consider giving your pie a top crust as opposed to a lattice or peek-a-boo crust. This covers all of the fruit filling, and showcase the pie’s taste.

Cook

• If using frozen berries to make your pie filling, consider heating them over the stove in a pot when combining with the other ingredients. Cooking the filling just a bit gives the flour more time to combine with the fat and the juices of the fruit. When cooking your filling, add whatever fat the recipe calls for, be it butter or cream, to combine with the flour. Constant stirring helpa to avoid lumps, but keep in mind that berries are a delicate fruit. Cooking the filling beforehand also negatea the need to increase your baking time if using frozen fruit.