Hello Sophie, that is a fantastic question and one that causes quite a bit of confusion depending on where you live or which recipes you are reading.
In the UK and Commonwealth countries, cornflour and cornstarch refer to the exact same ingredient. What you find labeled as cornflour on British supermarket shelves is pure starch extracted from the endosperm of the maize kernel. That chalky, fine white powder is precisely what was traditionally used to thicken custards, gravies, and puddings.
In North American cooking, however, the two are distinct products. In the United States, cornstarch is the pure white starch, whereas corn flour refers to whole dried corn kernels finely ground into flour. American corn flour contains protein, fiber, and fat, has a noticeable yellow tint, and tastes distinctly of corn, behaving much more like a fine cornmeal.
For your weeknight fakeaway, you want pure cornstarch (sold as cornflour in the UK). Because it contains no gluten and absorbs moisture efficiently, tossing your meat or vegetables in it before frying produces an airy, shatteringly crisp crust that stays light rather than heavy.
