Place a medium saucepan over medium heat for about a minute, then add the oil and swirl to coat the pan. Toss in the onion and dried herbs, and sauté for 5 minutes, or until the onion softens.
Stir in the garlic, and cook, stirring often, for another minute or so. Add the mushrooms and salt, stir to distribute, and cover the pot.
Cook for 10 minutes over medium heat, stirring once in a while, until the mushrooms give off a visible amount of their juices.
Meanwhile, place the cornstarch in a small bowl, and slowly pour in about a cup of the broth, stirring constantly with a small whisk until the mixture is completely smooth.
Pour the rest of the broth into the mushroom mixture and let it come to a boil uncovered over medium heat. When it boils, turn the heat to medium-low, and drizzle in the cornstarch slurry, stirring constantly with a wooden spoon.
Keep cooking, stirring very often, for another 10 minutes, or until the mixture is glossy and gently thickened. Add soy sauce to taste, if desired, and season liberally with black pepper. Serve hot.
Adapted from The Heart of the Plate by Mollie Katzen