Dried shiitake mushrooms are available in most supermarkets; fresh ones aren’t that easy to find. While dried shiitake is more convenient for storage purposes — keep them away from moisture and they can last for a couple of months — but there’s nothing like fresh shiitake. For some reason, even when soaked for hours, the texture and flavor of dried shiitake aren’t quite the same as fresh ones.
To prepare shiitake mushrooms — fresh or dried — the stems need to be cut off and discarded. Whether the caps need to be sliced or not depends on how they are intended to be cooked. For stir fries, fresh shiitake mushrooms are best when cut in bite-size pieces.