Dried mushrooms add dense flavour to stocks and stews. Many kinds can be easily bought - porcini from Italy, wood or cloud ear mushrooms from China and so on. It is actually very easy to dry your own. Since mushrooms are things which I readily keep in the house in case a gang descends, drying my own has become something that I do with the surplus which sometimes arises. Slice them, lay them out on a baking tray and put it into an over at 50 degrees C (I am lucky to have an oven which goes down to this low temperature.). This usually takes about 12 hours, but I check them from about ten hours onwards. Let them cool and you can either then store them in a jar, or grind them up to add to a stew or broth.