Let a 6.5kg turkey come to room temperature and rinse the entire bird. Season the skin with salt and pepper. Mix some softened butter with dried thyme and dried rosemary and rub all over the turkey. Carefully rub some under the skin of the breast.
Melt 120g of butter with 120ml of white wine in a bowl and add pieces of muslin to soak. Cover the breast and part of the leg with the muslin. Heat the oven to 220˚C/200˚C fan/gas mark 7 and cook on a rack in a roasting tin for 30 minutes. Reduce the temperature to 165˚C/145˚C fan/gas mark 3 and continue cooking for 3½ hours.
Every 30 minutes, use a pastry brush to baste the muslin and exposed areas of the turkey with the butter-and-wine mixture.
During the last 30 minutes of cooking, carefully remove and discard the muslin to brown the breast. Insert an instant-read thermometer into the thickest part of the thigh, avoiding the bone. When the internal temperature reaches 74˚C, the bird is done. Allow to rest for 20 minutes before carving to keep the turkey moist.