1 whole turkey (about 14 pounds), patted dry
2 tablespoons coarse salt
1 teaspoon black pepper
1 orange, halved
1 lemon, halved
1 small yellow onion, peeled and quartered
1 head garlic, halved
6 sprigs thyme
2 sprigs sage
1 tablespoon olive oil
3 cups chicken stock, warm
1/2 cup milk
2 tablespoons flour
Preheat oven to 425 with rack in lower third position.Season cavity of turkey with 1 tablespoon salt and 1/2 teaspoon pepper. Stuff cavity with orange, lemon, onion, garlic, and herbs.Tie legs with twine and transfer turkey to a rack set inside a roasting pan.
Rub skin with olive oil and season with remaining salt and pepper.
Pour 2 cups chicken stock into roasting pan and transfer to oven.
Roast turkey for 2 1/2 hours or until meat thermometer inserted into thickest part of breast registers 165 degrees. After first hour of roasting, baste turkey every 30 minutes, and tent with foil if skin becomes deep golden brown before turkey is cooked.
Remove turkey from oven and transfer to a carving board. Let stand at least 15 minutes.
Place roasting pan on stove top over medium-high heat and bring pan drippings and remaining 1 cup chicken stock to a simmer. Combine milk and flour in a mason jar and shake vigorously to combine. Whisk milk mixture into gravy and simmer, whisking constantly, until gravy thickens slightly, about 2 minutes.
Carve turkey and serve with gravy.