potato starch
Fine, pure white starch extracted from potatoes, known in Japan as katakuriko and the usual choice for coating and thickening.
In German-speaking countries potato starch sits in every supermarket's baking aisle, while in English-speaking countries it is more often found in Asian grocers, well-stocked supermarkets or online.
Substitute:
Cornstarch thickens sauces in much the same way, but gives a less glassy, crisp crust when frying and a slightly cloudier sauce.