Place all the marinade ingredients in a bowl, add the turkey pieces and leave to marinade for at least six hours or, preferably, overnight.
Heat a large pan or flameproof casserole and add a knob of butter. Add the pancetta and lightly brown then remove it from the pan and set aside. In the same pan, cook the mushrooms and onions for a few minutes until they colour then remove them from the pan and set the pan aside.
Remove the turkey from the marinade, strain the liquid over a bowl and discard the vegetables. Dip the turkey into the seasoned flour, shaking off the excess. Return the pan to the hob on a high heat and brown the turkey pieces on all sides. Turn down the heat and add the mushrooms, onions, carrot and celery along with the thyme and bay leaf. Pour in the strained marinade and simmer for one hour. Let the casserole rest for about 15 minutes then add the parsley and serve.