Dry-brine the turkey: Combine the salt, 2 teaspoons pepper and the chopped thyme and rosemary in a small bowl. Cut off the turkey legs (thighs and drumsticks together). Put the turkey breast and legs on a rimmed baking sheet. Season the turkey breast inside and out and the legs all over with the salt mixture. Stuff the turkey cavity with 1 halved garlic head, the halved lemon, 4 thyme sprigs and 2 rosemary sprigs. Cover and refrigerate overnight.
Position one oven rack in the bottom position and one right above it; preheat to 350˚. Combine the remaining halved garlic head, 4 sprigs thyme, 2 sprigs rosemary, the sliced lemon, bay leaves and shallot in a 9-by-13-inch baking dish. Add the olive oil and stir to combine. Place the turkey legs skin-side up in the baking dish and cover with foil.
Roast the turkey legs on the bottom oven rack until just tender when pierced with a sharp knife, about 2 hours. Uncover the legs and continue to roast until the skin is golden and the legs are completely tender, 1 to 1 1/2 more hours.
Meanwhile, for the turkey breast: Set a rack in a large roasting pan. Place the turkey breast breast-side up on the rack; let sit at room temperature 30 minutes. Once the turkey legs have been roasting for about 30 minutes, place the roasting pan with the breast on the rack above the legs; roast until the skin is deep golden brown and a thermometer inserted into the thickest part without touching the bone registers 160˚, 2 to 2 1/2 hours. Let the breast rest 30 minutes before carving. (If the turkey breast is done before the legs, move the legs to the higher rack to help them brown. If the legs are done before the breast is done resting, set aside and tent with foil to keep warm.)
Serve the turkey legs and breast with the roasted garlic, lemon and shallot.