Add the mushrooms to the skillet, season with salt and pepper and cook over high heat, stirring occasionally, until the liquid is evaporated and the mushrooms are golden, about 8 minutes. Stir in the shallot and garlic and cook for 1 minute. Return the onion to the skillet. Add the chicken stock and parsley and simmer over moderately high heat until the liquid is reduced to 1/4 cup, about 8 minutes. Add the remaining 2 tablespoons of butter along with the pistachios, lemon juice and chile and stir until the butter is melted. Season with salt and pepper.