To make the stuffing, heat the oil in a large frying pan and gently fry the chopped onion and crushed garlic for 5 minutes, until softened but not coloured. Add the sausage meat and cook over a medium heat for 10 minutes, stirring and breaking up with a wooden spoon. Tip into heatproof bowl and let cool for a few minutes.
Preheat the oven to gas 5, 190°C, fan 170°C and lightly oil a large, sturdy roasting tin.
Finely grate the lemon zest and squeeze the juice of both lemons. Cut one lemon skin into chunky pieces and set aside. Chop the sage leaves and roughly chop the chestnuts, then add to the cooled sausagemeat mixture along with the lemon zest and juice and the breadcrumbs. Stir well and season. Lightly beat the egg and stir into the stuffing mixture until well combined.
Remove any giblets that have been placed into the body cavity or neck of the turkey. Spoon half the stuffing mixture into the neck cavity. Bring the flap of skin down to cover the stuffing and secure with a metal skewer. Roll the remaining stuffing into balls, place on a small baking tray lined with nonstick baking paper. Cover with clingfilm and chill.
Put the bird, breast-side up, in the roasting tin. Put the pieces of lemon skin and bay leaves loosely inside the bird. Smother the turkey with the softened butter and season. Cover the turkey and tin with foil, pinching the edges to seal.
Calculate the roasting time according to the weight of your turkey. Roast for 20 minutes per kilo, plus 90 minutes. (If cooking a bird weighing 4kg or less, roast for 20 minutes per kilo, plus 70 minutes.) Roast for the allotted time, carefully removing and turning the tin every hour. Ovens and turkeys vary enormously, so check the bird after 2 hours and reduce the cooking time if it seems to be cooking faster than anticipated. If you wiggle one of the legs and it is a little loose, it is a good indication that the turkey is almost ready.
About 30 minutes before the turkey is due to finish cooking, remove the foil and continue roasting to brown the skin. Test if the bird is cooked by inserting a skewer into the thickest part of the leg. If the juices run clear the turkey is cooked. If not, simply pop it back into the oven for longer.
When the turkey is ready, transfer carefully to a platter. Cover with foil and let it rest for at least 20 minutes. Meanwhile, take the clingfilm off the stuffing balls and bake them in the oven for about 15 minutes, until cooked through and nicely browned.
To make the gravy, tilt the roasting tin and skim off any fat with a spoon. Put the roasting tin on the hob and sprinkle over the flour. Whisk the flour into the turkey juices and cook over a low heat for a minute or so, until thickened.
Slowly whisk in the wine or Madeira and bring to a simmer. Add 300ml (½ pint) water and return to a simmer. Cook for 3-4 minutes, stirring constantly, until the gravy has a good pouring consistency. Season to taste. (Add a splash of red wine or a few drops of gravy browning if the gravy is too pale.) Strain into a warmed jug or gravy boat. Carve the turkey and serve with the gravy and stuffing balls.
Turkeys are currently available in your local Tesco store.
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For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.