Place the salt, basil, bay leaves, peppercorns, mustard seeds, chile pepper, granulated garlic, granulated onion, ginger, lemon zest, cayenne pepper, water, and apple cider in a saucepan over medium-high heat. Bring to a boil and cook, stirring occasionally, until salt is dissolved. Remove from heat and cool to room temperature. Combine buttermilk and brine in a large container.

Place turkey in a well-scrubbed sink and cover with cold water; soak for 5 minutes, drain, and repeat process until water runs clear; trim off any excess fat and save for turkey stock.

Place turkey in a large brining bag and transfer to a large pot or container. Pour the buttermilk mixture over the turkey, press all the air out of the bag, and seal. Refrigerate for at least 24 and up to 36 hours, turning occasionally.

One hour prior to roasting, remove turkey from brine, discarding brine. Rinse turkey well and pat dry with paper towels. Place turkey, breast side up, on a rack in a heavy roasting pan.

Preheat oven to 325°F with an oven rack in the lowest position.

Mix together butter, thyme, sage, and black pepper. Gently loosen the skin over the breast, thighs, and legs and, using your fingers, push the herbed butter underneath the skin and in the cavities. Stuff cavities with onion and celery. Tightly cover breast with foil.

Place roasting pan in the oven and add 2 cups of stock to the pan.

Roast, basting the turkey all over with pan drippings every 30 minutes, replenishing with turkey stock as needed, until a quick-read thermometer reads 180°F in the thickest part of the thigh (see estimated roasting times here); remove foil for the last hour of roasting.

Remove turkey to a large serving platter and allow to rest for 30 minutes before carving. Reserve roasting pan and drippings for gravy.