Add the remaining 2 tablespoons of butter to the skillet and toss to coat the mushrooms. Cook, stirring a few times, until the mushrooms brown, about 4 minutes. Stir in the soy sauce, then add the sherry and cook over moderately high heat, scraping up the browned bits from the bottom of the skillet, about 1 minute. Add the cream and the reserved mushroom liquid and simmer over moderately high heat until thickened slightly, about 3 minutes. Stir in the parsley, season with salt and pepper and serve.