From: rec.food.cooking via Barbara Hlavin

Another interesting recipe is one that has become my favorite way for cooking
Spinach. If you like spinach, I believe you'll go nuts over this.

Wash and trim spinach leaves (fresh, obviously).  Slice shiitake mushrooms
and saute with a little butter and oil in a skillet until they have given
off their liquid, and that liquid has been reabsorbed.  Remove from skillet.
Now, add spinach leaves to the skillet and stir until wilted.  You'll need
to do this in batches; when one batch is wilted, move it to the side of the
pan and toss in the new leaves.  Repeat until all spinach has been wilted.
Now, throw in the shiitakes and toss with the spinach mixture.  Season with
fresh lemon juice (PLEASE...use the real stuff.  Nothing out of little 
plastic citrus-grenades or REAL GLASS bottles will do), and freshly ground
pepper.    

Note: I have used frozen spinach, and rehydrated shiitake mushrooms
sliced thin, sometimes mixed with ordinary mushrooms.  -sdh