1. 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, fill your kettle and boil it. Rinse the leeks well under a cold tap. Trim the roots and top 5cm off the leeks. Scrub, trim and peel the carrot. Keep all the trimmings. Pop the trimmed veg aside to make the gravy later. Pour 1 tbsp 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. Pour the cider into the pan with the giblets and bring to the boil. Add the trimmings from the leeks and carrots and drop in the bouquet garni. Top up with 400ml boiling water. Return to the boil, then cover the pan, reduce to a simmer and cook for 1 hr. When cooked, strain it through a sieve into a jug.
4. While the stock simmers, heat your oven to 180°C/Fan 160°C/Gas 4. Weigh your turkey to check how much it weighs exactly. Pop it into a large roasting tin, breast-side down. Pour 500ml boiling water around (but not over) the turkey. Season with a little salt and pepper. Put 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).
5. After 1 hr, take the turkey out of the oven and carefully turn it over so it’s breast-side up (make sure to protect your hands from the heat and have some sturdy spatulas to help with turning it). Season the turkey again. Use a sharp knife or skewer to slice right through the skin between the leg and breast to allow the juices to drain out and the thighs to cook. Top up the liquid in the tin with 250ml boiling water.
6. Return the turkey 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 cranberry stuffing. Open the packet and pour the contents into a bowl. Add 30g butter (save the rest of the butter for the gravy) and pour over 200ml boiling water. Stir well and let stand for 5 mins. Scoop the stuffing into a small ovenproof dish and roast for 25-30 mins till browned and crisp. Remove from the oven and cover with foil. Set aside to keep warm.
8. Meanwhile, finish the gravy. Finely slice the trimmed leeks. Finely dice the trimmed carrot. Peel and finely chop the garlic cloves. Melt the remaining 50g butter into a pan and warm to medium heat. Slide in the leeks, carrot and garlic, and season with pinch of salt and pepper. Cook gently for 10 mins, stirring occasionally, till softened.
9. Stir 2 tbsp flour into the softened veg and cook for 2 mins. Slowly pour in the 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.
10. To check the turkey is ready, insert a skewer into one of thighs. If the juices run clear, it’s ready. Transfer the turkey to a board. Wrap loosely in foil and rest for 1 hr. Pour the roasting tin juices into a measuring jug. Let it sit for 15-30 mins so the fat rises to the surface. Skim off the fat. Pour the roasting juices into the gravy, stir well then reheat. Taste the gravy and add more salt or pepper if needed. Serve the roast turkey with the gravy and cranberry stuffing.