The robust, earthy flavors of this soup qualify it as a special winter elixir. I usually use a rich beef broth for the base, but I didn't have any beef broth handy. What I did have was turkey broth--lots and lots of turkey broth.
There is nothing difficult about this soup as long as you have the mushrooms, the barley and maybe an onion. We had perhaps a half-pound of mushrooms--creminis and shitakes--left over from the mushroom pate my wife made for a recent cocktail buffet. The barley is a pantry staple around here. And it turned out I only had half an onion, but lots of shallots. So I substituted three or four shallots for the missing onion half.
In your largest cast-iron skillet, saute about four cups of mushrooms cut into 1/4-inch slices. I like to start the mushrooms in a smoking-hot skillet to brown them a little, then turn the heat down to finish cooking. They will soak up lots of extra-virgin olive oil, so don't be afraid to add more. It will just make the soup that much richer. Season aggressively with salt and pepper.
Meanwhile, in a heavy pot or Dutch oven, saute the onion (or shallots), cut into medium dice, and three or four cloves of garlic, thinly sliced, with about 3 tablespoons extra-virgin olive oil. Season with salt to draw the juices out. In a saucepan, cook 1 cup pearled barley with 2 cups turkey stock (or substitute beef or chicken stock) seasoned with salt.
Naturally, these three items will cook at different rates, so time it how you please. (Since the barley soaks up so much stock, I cook it separately.) You just want the onions in the soup pot soft, then you can add the sauteed mushrooms and the cooked barley and finally 8 cups stock of your choice. Add 1/4 cup sherry and cook another 20 minutes or so over low heat just to infuse the soup with the flavor of the mushrooms and the sherry. The soup will be even better made a day ahead.
Serve hot with a salad from the garden and a slice of sourdough bread.