potato starch
Fine white starch powder from potatoes, used in Japan as katakuriko for thickening and coating.
In German-speaking countries potato starch sits in the supermarket baking aisle; in English-speaking countries look in Asian grocers, health food shops or online, often labelled katakuriko.
Substitute:
Tapioca starch comes closest. Cornstarch also thickens, but gives cloudier, less glossy sauces and fried coatings that are less crisp.