Cornstarch is the American name for the fine white powder made from maize that cooks use to thicken soups, sauces, and some puddings. It is the same kitchen powder British English calls cornflour. You mix it with cold water first, then stir it into hot liquid; if you dump the dry powder straight into a hot pan it goes lumpy. It has almost no taste. Though actually, it is not cornmeal (that is coarser, for bread and coatings), and it is not Taiwan’s 太白粉, which is usually potato starch. Both thicken, but they come from different plants and do not behave in quite the same way in the pan.