Preheat the oven to maximum. Heat a saucepan at medium heat and add a drizzle of olive oil and the sage leaves.
Peel and chop 2 garlic cloves and 1 onion. Add the garlic, celery and onion to the saucepan and fry everything gently until soft and golden. Take the pan off the heat, add the breadcrumbs and, while the mix is cooling down, add the cranberries and stir them in. When the stuffing has cooled down, add the lemon zest, nutmeg, and lots of salt and pepper, and mix everything together well.
Chop the remaining onions in half and slice the carrots lengthwise.
Place your turkey on a board, with the neck end towards you. Find the edge of the skin that’s covering the turkey’s breasts and gently peel it back. Work your fingers and then your hand under the skin, freeing it from the meat. If you’re careful you should be able to pull all the skin away from the meat, keeping it attached at the sides. Go slowly and try not to tear it! Lift the loose skin at the neck end and spoon the stuffing between the skin and the breast, tucking the flap of skin underneath to stop anything leaking out. Put the halved orange in the cavity along with some onions, garlic and rosemary. Weigh the stuffed turkey and calculate the cooking time (about 20 minutes per 500g).
Place the turkey on a large roasting tray, rub it with olive oil and season well. Surround with the chopped carrots, onions, remaining garlic, cover with foil and place in the preheated oven. Turn the heat down right away to 180°C, and roast for the calculated time, or until the juices run clear from the thigh if you pierce with it a knife.
Remove the foil for the last 45 minutes to brown the turkey.
Carefully lift the turkey out of the tray and rest on a board that’s covered loosely with foil for at least 1 hour.
When the resting time’s nearly up, skim the surface fat from the roasting tray and add the flour and stock. Place the tray on the fire and bring to the boil on a high heat. When the gravy starts to thicken, strain it into a bowl. Carve your turkey, serve with the gravy!