Mix the chestnut puree with the veal demi-glace. When smooth season with salt and pepper and add the softened butter.
Place 3 tablespoons clarified butter into a frying pan and add diced onion. Saute lightly. Cut bacon into fine strips and add to the onions. Fry together for 1 minute. Remove from the heat and place into a bowl with the chopped parsley. Season with salt and pepper and add the ground pork. Combine ingredients with an egg and mix well.
Place the onion into some of the clarified butter in a saucepan and allow to fry. Add the chopped turkey neck and brown. Add the water, bay leaves and thyme. Simmer the stock uncovered for 1 hour. After this time add 1/4 cup port and simmer for 5 minutes. To make the gravy, remove fat from baking pan and deglaze with the turkey stock. Serve gravy separately in a sauceboat.
For the turkey: Preheat the oven to 325 degrees. Paint grill rack with clarified butter. Place the chestnut dressing in the neck opening, pressing it in firmly. Place the pork dressing in the rear end. Truss the turkey. Lightly flour breast. Place the turkey on its side on a grill rack in a baking dish and bake for l hour. Turn the turkey onto the other side and roast for 1 hour. Turn the bird breast side uppermost and paint with clarified butter and season with salt and white pepper. Roast for a further 2 1/2 hours basting every 30 minutes with clarified butter.
Recommended drink: Good dry red wine, Claret style