Photograph: Jonathan Gregson
For the stuffing, melt the butter in a frying pan and fry the onion, celery, garlic and celery salt for 8-10 minutes or until soft; cool. Blitz the bread to crumbs in a food processor and tip into a bowl, then blitz the pistachios and mix thoroughly with the remaining stuffing ingredients and the onion mixture.
Preheat the oven to 190°C, fan 170°C, gas 5. Pat the turkey all over with kitchen paper, then stuff the breast from the neck end with roughly half of the stuffing mixture. To do this, loosen the skin with your hands, gently easing it away from the flesh, then carefully push the stuffing under the skin and towards the breast. Pull the skin neatly back over the stuffing. Transfer the turkey to a large roasting tin, spread the soft butter all over it and season.
Cover the turkey with kitchen foil and roast it for 3 hours, basting it periodically with the cooking juices. Remove the foil one hour before the end of the cooking time. While the turkey is cooking, cook the clementine halves on a hot griddle pan until caramelised; set aside. Roll the remaining stuffing into 12 balls and wrap each in a piece of bacon. Put a sage leaf on each chipolata and wrap in a piece of bacon, too.
To check if the turkey is cooked, pierce the thickest part of the leg with a knife – if the juices run clear, the turkey is ready. When cooked, transfer the turkey to a platter (reserve the tin with the juices for the gravy) and cover loosely with kitchen foil and leave it to rest for up to an hour. Increase the oven temperature to 200°C, fan 180°C, gas 6. Put the stuffing balls and chipolatas on a baking tray and cook for 30 minutes.
To make the gravy, put the roasting tin with the turkey juices over a high heat. Add the white wine and reduce for 5 minutes until syrupy. Add the stock, herbs and Marmite to the tin and simmer gently for 15-20 minutes. Pass through a sieve and return to the tin. Mix the cornflour with a little water to form a paste, then whisk into the tin – continue whisking until the sauce thickens. Season to taste.
Arrange the clementines, bay leaves, stuffing balls and chipolatas around the turkey and serve with the gravy.
Get ahead: prepare the turkey the day before and chill overnight; bring to room temperature (allow 2-3 hours) before you roast it.
Kitchen secret: carve the turkey at the table or, if you find it easier, transfer it to a board to carve. Start by thinly slicing the breast meat in a downwards motion. The most important thing is to use a sharp carving knife and the rest will be easy. Remove the turkey legs, one by one, holding the leg up so you can place the knife in the joint.