Dehydrating white onions by using a hydroscopic method removes the liquid but leaves behind the flavor. These can be reconstituted and then used as you would a fresh onion. To reconstitute, soak in water for fifteen to twenty minutes. Drain any excess liquid before use or save this liquid to add some extra flavor to soups, stocks, gravies or sauces.
About 5 tsp. dried white onion will yield ¼ cup re-hydrated onion. Use these in a pinch or for everyday use. The flavor is so good nobody will be the wiser and you will save plenty of time and avoid all the mess of slicing onions.