Herb Butter: Mix all the herb butter ingredients together. Set aside.
Preheat oven to 220 degrees C.
Turkey: Rinse turkey under cold water and dry with kitchen towels. Rub the insides with salt and pepper.
Carefully peel back skin of the turkey on the breast side as far down the sides as possible (try not to tear). Do this by running you fingers under the skin. When the whole skin is loose, put two thirds of the herb butter under the skin.
Tie legs and wings together with cooking twine so that the turkey is as tight as possible and won't dry out.
Place turkey breast side up in a baking tray and cover loosely with foil. Transfer to oven and reduce the temperature to 180 degrees C. Cook for 3 hours.
Remove foil. Spread the remaining herb butter on the turkey and cook for another 45 minutes, basting occasionally. Continue cooking turkey until the internal temperature reaches at least 80 degrees C, checked with a meat thermometer. Recover with foil and let stand for 30 minutes before carving.
Meanwhile, skim fat off the drippings. Pour through a sieve into a small saucepan and bring to the boil. Depending on the amount of gravy, add 1-2 tablespoons cornflour mixed with a little water. Stir until smooth and heat until thick. Serve with turkey.