Brine it in a big bag with as much water as is needed to immerse it. 60gram of salt every liter. Add 1 head of garlic, crushed, skin on (while head, not a clove hor). Chop up an onion and 2 shallots, 2 sprigs of Rosemary and thyme. 2 green apples.
Put the whole bag into the fridge and keep it there 36 hrs. Take it out on Christmas Day am. Take turkey out. Tosh out the brine and the herbs, fruit and veg. Use same bag, fill with plain water. Immerse turkey in bag, go back to fridge 1 hour. Take it out, change the water, put back to fridge again another hour. Do it once more (3 water changes). Your turkey is now wet and moist. Put on roasting pan. Pat dry.
Put 5 shallots, 2 cloves of garlic, 150 grams of pancetta ham, 3 sprigs of thyme (leaves only), 1 sprigs of Rosemary (leaves only), 6 sprigs of sage, 200 grams of butter (unsalted), 50 grams of grated Parmesan, 50 ml olive oil, fresh cracked black pepper, salt - all into your blender. Blitz till fine and like a paste. Once ready, rub turkey all over. Inside the cavity as well. Make sure you get the mix into the parts below between the flesh and skin at the breast and the legs. This will keep turkey moist when cooking.
Stuff 2 chopped green apples, 2 crushes garlic cloves, and a shallot or two halves) into the cavity. Tie the bird up.
Turn oven up to 130, roast for 3 hours. Baste regularly with the juices. Take out of oven, rest turkey for 30 minutes. Turn up temperature to 200 deg. Put turkey in oven again. You'll need another hour or so, watch to make sure the skin doesn't burn. Take out after an hour, check meat thermometer for temp to register 70 deg C in thickest part of the turkey. If not, pop it back in and roast till you hit 70 deg C. You're done then. Take it out. Let it rest on a plate. With the juices that's in the roasting pan, you can do up a parsnip or roasted potato salad. That's another story. But this is basically it.