Cornflour is a starchy flour made from maize. It is mostly used as a thickening agent: when mixed with a liquid and heated, it thickens rapidly without altering the flavour.
If you intend to buy: Cornflour is available as a white powder, sold in packets or tubs of varying size.
If you want to use it: To add cornflour to a liquid, it is best to mix the powder in a little water or other liquid first before adding this mixture to the larger quantity of liquid to be thickened.