1. Around 2 hrs before you want to roast your turkey, take it out of the fridge and let it stand somewhere safe so it can come to room temperature. Take the giblets out of the turkey, and rinse them.
2. While the turkey comes to room temperature, make a giblet stock. Fill your kettle and boil it. Peel and thickly slice the onion. Scrub and thickly slice the carrot. Trim the celery and roughly chop it. Pour 1 tbsp olive oil into a pan and warm to a medium-high heat. Add the giblets. Season with salt and pepper. Fry for 3-4 mins, turning, till browned.
3. Add the onion, carrot and celery to the pan. Drop in the bouquet garni. Pour in 800ml boiling water. Bring to the boil, then cover the pan with a lid, reduce to a gentle simmer and cook for 1 hr. When cooked, strain the stock into a jug.
4. While the stock simmers, heat your oven to 180°C/Fan 160°C/Gas 4. Make the clementine and bay leaf butter: finely grate the clementine zest into a bowl, then slice the clementines horizontally into thick rounds and spread them out in a large roasting tin. Set aside. Snip 3 bay leaves into fine shreds and add them to the bowl. Add 50g of the butter with a pinch of salt and pepper and mash together with a fork.
5. Weigh your turkey to check its exact weight. Pop the turkey on top of the clementines, breast-side down. Pour 500ml boiling water around (but not over) the turkey. Pop the turkey in the oven on the middle shelf. Roast for 1 hr (this is the same, whether your bird weighs nearer 4kg or 5kg).
6. After 1 hr, take the turkey out of the oven and carefully turn it over so it’s breast-side up (protect your hands from the heat and have some sturdy spatulas to help turn it). Dot the clementine and bay butter over the top of the turkey. Use a sharp knife to slice through the skin between the legs and breast to allow the juices to drain out and help the thighs to cook. Insert the meat thermometer into a thigh. Top up the liquid in the tin with 250ml boiling water. Return to the oven and roast for another 1 hr. If your turkey is closer to 4kg, then you only need to roast it for 45 mins more.
7. When the turkey has 40 mins remaining, make the herby lemon stuffing. Open the packet and pour the stuffing mix into a bowl. Add 30g of the butter and pour over 300ml boiling water. Stir well and let stand for 5 mins. Scoop the stuffing mixture into a small ovenproof dish and bake for 25-30 mins till browned and crisp. Remove from the oven and cover with foil. Set aside to keep warm.
8. Meanwhile, make the gravy. Melt 20g butter in a pan and warm to medium heat. Stir 2 tbsp flour into the melted butter and cook, stirring, for 2 mins. Slowly pour in the strained giblet stock and stir to incorporate. Bring the pan to a gentle simmer and cook for 20 mins, till the gravy has thickened, then set aside, lid on.
9. When the meat thermometer hits 60-65 °C (remember to check the weight of your turkey), transfer the turkey to a board, wrap loosely in foil and rest for 1 hr. Pour the roasting juices into a jug, discarding the clementines. Let it sit for 15-30 mins so the fat rises to the surface. Skim off the fat. Pour the juices into the gravy, stir then reheat. Serve the turkey with the gravy, the herby lemon stuffing and the cranberry sauce.