Start the barley by combining it with 4 to 6 cups of water in a pot. Bring to a simmer and cook until the barley is almost tender, soft enough to eat but still with a slight bite.
In a separate pot, melt the 12 tablespoons butter over medium heat. Add the 2 large coarsely chopped onions and 3 cloves of chopped garlic. Sauté until the onions are soft and translucent. Stir in the 1 pound crimini mushrooms and salt, then continue to cook until the mushrooms release their liquid and turn a deep brown. Deglaze the pan with the 4 tablespoons sherry and 4 tablespoons soy sauce, scraping up any browned bits from the bottom of the pot.