Step 1Combine the kosher salt, tamari, sugar, thyme, allspice, pepper flakes, fennel seeds, cumin seeds and peppercorns in a stockpot large enough to hold the turkey. Add 2 gallons cold water. Bring to a boil, then remove from the heat and cool completely. Add the garlic and ginger.
Step 2Rinse the turkey inside and out. Lay it breast-side down into the cold brine. Refrigerate 12 hours, then turn the turkey so that the legs are immersed in the brine. Refrigerate 12 more hours.
Step 3Heat the oven to 500 degrees. Remove the turkey from the brine and drain well, then wipe clean; pat dry. Discard the brine.
Step 4Loosely fill with stuffing. Lay on a rack in a roasting pan. Rub with soft butter. Season with salt and pepper. Roast 30 minutes.
Step 5Reduce the heat to 350 degrees. Roast, basting every 30 minutes with pan drippings, until a meat thermometer inserted in thickest part of the breast registers 180 degrees, about 3 to 3 1/2 hours.
Step 6Remove the turkey from the oven and spoon the stuffing into a heatproof dish. Cover the turkey with a tent of foil and let it sit 30 minutes before carving.