Reposting this tip because it saved me once again this year...
(I even stock up on extra potato starch Post Pesach...while it is still available.)
So you went out and bought a new bag of flour right after putting away the Pesach dishes. Now both you and your kitchen are ready to get back to baking challah— and just in time for Shlissel Challah Shabbos. But once you've got your dough mixed, you find that it's a bit sticky and—uh-oh! You only bought that one bag of flour to work with. There is no other flour in the house. Zero. Guaranteed. What do you do now? Solution: You certainly have some potato starch left over from Pesach. Not only is that leftover potato starch a perfect substitute for the little bit of extra flour that you need to ‘un-sticky’ the dough, it may do more good than you think! In fact, for years, people have intentionally added ‘potato-water’ to their bread dough for a light, fluffy texture.
Potato water is just the cloudy water that’s left in the pot after you boil potatoes. It’s starchy and thicker than plain water and may have tiny bits of potato floating around in it. The reason potato water works well to help your bread rise is because it has potato starch in it! The starch encloses the gas bubbles in your dough and strengthens them. That allows your bread to rise lighter and higher. Your added potato starch can have a similar effect. Next time you bake, if you are still left with lots of potato starch, you can try replacing half a cup of flour with an equal amount of potato starch. And once you have used up all the potato starch from Pesach, make some potato water and substitute some or or all of the water in your recipe with that. Just be sure to scrub those potatoes very well or peel them before boiling. Happy Baking!