When I was at HTLA Chef Eric (from Millenium) told me to save my mushroom stems and make a broth with them. Since I love a good mushroom stock and I also love getting the most out of all my produce -- I just had to try this!
Sadly, I just haven't had any mushroom butts to try give it a go... until now!
Having made a beautiful mushroom gravy for Thanksgiving (Thanksgiving Gravy pg.255 HHC), I had a lot of bottoms leftover and threw them in a pot with 4 cups of water and some chopped onion (also Eric's suggestion).
I brought it to a boil, then simmered for about an hour -- until the onions were practically falling apart.
I drained the stock off then pressed excess liquid out with a bowl.
Tada! Mushroom stock.
I also added a bit of low sodium soy sauce -- but it wasn't necessary and you could use salt or miso.
Now it's time for soup!