For thickening sauces, what is the difference between plain flour, cornflour and arrowroot?
Plain flour is usually used as the base for a sauce to form a roux (combination of butter and flour) to which milk or stock is added, stirred, and brought to the boil to thicken. Cornflour is usually added in the form of a paste mixed with water to dishes at the end of the cooking time to thicken. The same applies for arrowroot, but it is used when a clear sauce is required (such as for sweet and sour) as cornflour paste gives a cloudy end result.