On the day before cooking, spatchcock the turkey by placing it on a chopping board, breast-side down. Score along each side of the spine with a sharp knife or a pair of poultry shears (there should be little to no resistance), remove and reserve the bone for making stock. Flip the bird back over so it’s breast-side up and press down until the breast bone cracks and the turkey can be flattened.
Move to a roasting tray large enough for the spatchcocked turkey and sprinkle with baking powder, orange zest, and a good covering of black pepper. Place half of the thyme and sage on the turkey’s surface and completely cover the bird with fine salt. Refrigerate for at least 12 hours and up to 24.
Once the turkey has cured, pre-heat the oven to 200C/Gas 6.
Rinse the dry cure from the turkey, pat dry with kitchen paper, and move the turkey, skin-side up, to a baking tray. (If you have a baking tray with a rack, that would be ideal, but it’s not absolutely necessary).
Drizzle a little oil over the skin, and place in the oven for 90 minutes.
While cooking, baste a few times, then 20 minutes before it’s cooked, add the melted butter and the rest of the thyme and sage. Cook until the skin is crispy and the thickest part of the thigh meat registers at 175F. (If you don’t have a meat thermometer, check that the juices run clear and no pink flesh remains.)
Rest the turkey for 30 minutes then carve and serve.