Take your turkey out of the fridge at least 1 hr before you cook it. Heat oven to 200 C/180 C fan/ gas 6 and beat the butter with the rosemary. Starting from the neck of the turkey, carefully push your fingers underneath the skin until you can get your whole hand between the skin and the breast meat. Trying not to tear the skin as you go, spread the butter inside the pocket, squishing some into the crevice between the thigh and breast meat.
Put the garlic, lemon and bay leaves inside the turkey, then season liberally all over. Put the shallots in your largest flameproof roasting tin and put the turkey on top, breast-side up. Roast for 1 hr, then give it a good baste, pour in the wine and nestle the cabbage wedges in the tin (or underneath the turkey if they won’t fit). Return to the oven for another 30 mins – covered with foil if the turkey is looking too brown. The juices should run clear when you pierce the thickest part of the thigh, or a thermometer should read 75 C. If not done, carry on cooking for a further 5-10 mins.
Set aside the turkey on a board to rest for 1 hr, transferring the garlic and bay to the roasting tin for the gravy. If you want crispy skin, don’t cover the turkey. Wrap the cabbage wedges in two parcels of foil, with a spoonful of the turkey juices, season liberally and return to the bottom of the oven to carry on cooking while the turkey rests.
Spoon away most of the turkey fat, then put the tin on the hob over a medium heat. Mash the veg with the back of a wooden spoon to extract as much flavour as possible , then pour in the stock and reduce the gravy by half. If you want to thicken it, stir in the cornflour mixed with 1 tbsp water. Once happy with the consistency, strain and keep warm until ready to eat.