1. Preheat oven to 350 degrees.

2. Make the turkey: In a small bowl, combine sugar, 4 1/2 teaspoons salt, chili powder, paprika, cumin, sage, and 2 1/2 teaspoons pepper in a small bowl. Set aside about one-quarter of the seasoning mixture for the pan-roasted onions.

3. Trim turkey's tail fat and set aside. Trim and discard any remaining fat and remove and discard giblets. Place orange, onion, and sage sprigs in cavity of turkey; season cavity with salt and pepper. Generously pat remaining rub over turkey. Set aside.

4. Make the pan-roasted onions: Place sliced onions in the center of a large roasting pan to make a bed for the turkey; season with reserved spice mixture. Mince reserved tail fat; add to roasting pan along with butter. Set turkey directly on top of onions.

5. Transfer roasting pan to oven, legs first, and roast turkey until a meat thermometer inserted into the thickest part of the thigh registers 155 to 165 degrees, 2 to 2 1/2 hours. Remove roasting pan from oven and transfer turkey to a carving platter; tent turkey with foil and let stand 10 minutes.

6. Transfer onions to a serving dish; squeeze orange over onions and add any drippings that have collected under turkey on carving platter. Carve turkey and serve with onions.