Preheat the oven to 190°C, fan 170°C, gas mark 5. Heat the oil and butter together in a large saucepan, then add the onion, garlic and celery.
Fry over a moderate heat for 3-5 minutes until softened, then add the chestnuts and cook until they begin to brown. Remove from the heat and set aside. Squeeze the meat out of the sausages and discard the skins, then set aside.
To make the stuffing, place the breadcrumbs in a large bowl, sprinkle with the xanthan gum and mix well. Add the chestnut mixture, sausagemeat, apple, orange segments, sage and lemon zest and juice.
Season with freshly ground black pepper and mix to combine. Allow to cool slightly before shaping into rounds, about the size of golf balls, then cover and refrigerate until needed.
Meanwhile, remove the giblets and the neck from the turkey cavity (you could use these to make a turkey stock or gravy). Wash the turkey and dry well with kitchen paper.
Place the turkey in a roasting tin and cover with lightly greased foil. Place in the oven and roast for 2 hours and 5 minutes, then remove from the oven. Remove the foil from the turkey, then add the stuffing balls to the roasting tin and return to the oven for the remaining 45 minutes.
Remove from the oven, cover with foil and leave to stand for 30 minutes before carving, then serve with all your favourite trimmings.
Cook's tip: Always check that the turkey is cooked thoroughly and that the juices run clear when a skewer is inserted into the thickest part of the meat. If you have a larger turkey you will need to alter the cooking time accordingly - refer to the pack instructions for how to calculate the time.
What size turkey should I buy?
3kg: 6-7 people; 3.5kg: 7-8 people; 4kg: 8-9 people; 4.5kg: 9-10 people; 5kg: 10-11 people; 5.5kg: 11-12 people; 6kg: 12-13 people; 6.5kg: 14-15 people; 7kg: 15-16 people; 7.5kg: 16-17 people.
* Allergen information: Customers are advised to check allergen warnings on products at the time of purchase as allergen information on products is subject to change after publication of this recipe.