Preheat the oven to 425°F. In a small bowl, combine kosher salt, black pepper, onion powder, garlic powder, dried sage, dried thyme, smoked paprika, cayenne pepper, and allspice. Rub seasoning all over the outside of the turkey, inside the cavity of the turkey, and under the turkey skin to permeate the breasts, thighs, and drumsticks. Reserve about 2 tablespoons of the seasoning for the butter mixture. If brining the turkey, store in the fridge for up to 48 hours.
Combine butter with olive oil, minced garlic, and the remaining spice blend. Make sure to save 4 tablespoons of butter for the gravy. Cover the turkey with the buttery mixture, making sure to get under the skin. Add onion, garlic, celery, carrots, lemon, and herbs to the bottom of a roasting pan, and inside the cavity of the turkey. Place the turkey over top of the vegetables. Tie the turkey legs together with kitchen twine.
Place the turkey in the preheated oven and roast for 30 minutes, then, without opening the oven door, drop the oven temperature to 325°F and continue roasting for an additional 2+ hours, until the turkey reaches an internal temperature of 165°F in the thickest part of the thigh. The cooking time will depend on the size of your turkey. Baste the turkey with the pan drippings every 30 minutes or so.
While the turkey rests, make the gravy. Add the remaining butter to a large saucepan and melt it over medium heat. Slowly add in flour and mix vigorously to ensure there are no clumps. Now, add in the pan drippings from the bottom of the roasting pan. Mix in Worcestershire sauce, and add salt, pepper, and seasonings to taste. Continue mixing until a smooth gravy forms, then remove from heat. Serve, and enjoy! Store leftovers in the fridge for up to 5 days.