Potato starch is the extracted starch from potatoes. The starch turns to a light, powdery, flour-like consistency once it has dried out, and it is a common ingredient that features in several recipes.

If you’ve ever grated a pound of potatoes—say, for latkes—and soaked them in water until you’re ready to fry, you may have noticed some white, powdery stuff sinking to the bottom of the bowl. That, my ...