Cornflour is a thickener that comes from the starch of corn or wheat. It has twice the thickening power of flour, without adding any flavour to the dish. Cornflour produces sauces that are almost clear. Asian sauces often are thickened with cornflour, which gives them a glossy and clear quality. Flour, more commonly associated with gravy, makes a recipe opaque or milky in appearance.

A slurry is a mixture of cornstarch and cold liquid mixed together until smooth. Always dissolve cornflour in a cold liquid before adding to a hot mixture or the cornflour will lump. After stirring the slurry into a hot liquid, bring it to a boil and simmer until the mixture thickens.

When a fruit pie recipe seems to call for a good amount of cornflour, there's a reason for it. If you use cornflour to thicken something containing citrus or apple juices, such as a pie, it's thickening powers are cut in half.

Add a cornflour slurry near the end of the cooking time so you don't overcook the cornflour. Overcooking can lead to a thinning of the sauce.

Cornflour usually has a "best used by" or "best purchased by" date on the box. Unopened, it should keep in a cool, dry place for a year or two.

For every 1 tablespoon of cornflour called for in a recipe, substitute 2 tablespoons of plain flour.