Leeks have a mild onion-like taste to them and compliment a lot of different dishes. I mainly use them in soups, stews, and casseroles. You can use them in place of an onion in any recipe you see fit. They dehydrate easily and can be rehydrated quite easily.
To dehydrate a leek, first cut off the ends of the leeks, including the green ends. Wash well. Slice the leeks about 1/8"-1/4" thick. Once they are all cut up, run the slices under water or soak for about 5 minutes. You soak them to get all the dirt off of them. Lay the leek pieces on your dehydrator tray and dehydrate at 125 degrees for about 8-10 hours. I generally just turn on my dehydrator before I go to bed and they are ready the next morning.