Heat the butter in a deep frying or sauté pan until sizzling, then add the mushrooms and fry for 4-5 mins until softened. Sprinkle over the flour and stir until a paste forms. Cook for a few more minutes.
Splash in the wine or sherry and let it bubble for a minute, then stir in the stock and bring to the boil. Reduce the heat to a simmer and stir in the cream. Season, then stir in the turkey. Simmer until the turkey is heated through, then remove from the heat and stir in the parsley, if using. Serve with pasta, mash or rice.