1 (12- to 14-pound) turkey, thawed if frozen
1 tbsp. Dijon mustard
4 tbsp. olive oil
¼ bunch fresh flat-leaf parsley
3 medium onions, cut into wedges
4 sprigs fresh rosemary
¼ cup fresh sage leaves, chopped
4 cloves garlic, finely chopped
2 medium carrots, cut into 2-inch pieces
2 stalks celery, cut into 2-inch pieces
¾ cup low-sodium chicken broth
Heat oven to 375ºF. Working on a baking sheet, remove the giblets and neck from the cavities. Reserve the neck (and the giblets, if desired). Using paper towels, pat the turkey dry. Using a vegetable peeler, remove 6 strips of zest from the lemons. Finely chop the zest (you should have about 2 tablespoons). Halve the lemons and squeeze 2 tablespoons juice into a small bowl; whisk in the mustard and 2 tablespoons oil. Remove the leaves from the parsley and stuff the stems in the cavity along with the lemon halves and half the onions. Finely chop the parsley leaves and the needles from 2 sprigs rosemary. Add to the bowl with the lemon zest, along with the sage and garlic.
Carefully slide your fingers under the skin of the turkey breast and thighs to loosen it. Stuff the herb mixture under the skin. Tie the legs together with kitchen twine. Tuck the wing tips underneath the body (this will prevent them from burning). Rub the turkey with the remaining oil and sprinkle with 2 teaspoons salt. Place the turkey neck, carrots, celery, the remaining onions, and the remaining 2 sprigs rosemary in a large roasting pan. Place a roasting rack in the pan and put the turkey on top of it. Roast the turkey until a thermometer inserted into the thickest part of the thigh registers 165ºF, 2 ½ to 3 hours. (Cover the bird loosely with foil if it browns too quickly, and add the broth to the pan if the vegetables begin to scorch.) Carefully tilt the turkey to empty the juices from the cavity into the pan. Transfer the turkey to a carving board or cutting board set in a rimmed baking sheet (to catch juices while carving). Cover loosely with foil and let rest for at least 25 minutes. Reserve the pan and its contents for gravy. Carve the turkey as desired. Garnish with fresh rosemary, if desired. Serves: 8.