Melt the butter in a large enameled cast-iron casserole. Add the shallots and garlic and cook over moderate heat, stirring occasionally, until softened but not browned, about 3 minutes. Add all of the mushrooms and season with salt and pepper. Cook over moderately high heat until the mushroom liquid has evaporated and the mushrooms are lightly browned, about 8 minutes. Add the sage and wine and cook until the liquid has reduced by half, about 2 minutes. Add the stock and simmer for 2 minutes, then add the cream and simmer until slightly thickened, about 2 minutes longer. Season with salt and pepper and stir in the parsley. Remove from the heat and keep warm.