corn flour
Finely ground whole maize, yellow or white; not the same as cornstarch, which British English also calls cornflour.
Fine maize flour is sold in health food shops, in the gluten-free aisle, and in Latin American or Turkish grocers, while ordinary supermarkets often stock only coarser cornmeal or polenta. In the UK, look for fine cornmeal or maize flour, because a packet labelled cornflour there is pure starch.
Substitute:
Fine cornmeal or polenta, ground a little finer in a blender, works well but gives a grainier, more crumbly result. Cornstarch is not a substitute.