How to Make It
In a heavy nonstick skillet large enough to hold the mushrooms in a layer no deeper than 1 1/2 inches, combine the butter with 3 tablespoons of water and bring to a boil over high heat. Stir in the mushrooms, salt and pepper and cook until the mushrooms have released their juices, 10 to 12 minutes. Continue to cook, stirring frequently, until the juices have evaporated, 5 to 7 minutes. Reduce the heat to moderate and cook, tossing frequently, until the mushrooms have caramelized to a deep brown, 20 to 25 minutes.
Stir the parsley, shallots and garlic into the mushrooms. Add enough water to just cover the mushrooms and stir, scraping up the browned bits from the bottom of the pan with a wooden spoon. Bring to a boil, then reduce the heat and simmer until the liquid is reduced by half and the broth is deep brown, about 25 minutes.
Strain the broth through a fine sieve, pressing firmly on the mushrooms to extract as much liquid as possible; discard the mushrooms. Season the broth with pepper and the soy sauce.