Crisp-Skinned Spatchcocked (Butterflied) Roast Turkey With Gravy

Name: Crisp-Skinned Spatchcocked (Butterflied) Roast Turkey With Gravy
Prep time: 15 min
Cook time: 105 min
Total time: 120 min
Yield: 12
Ingredients: 3 large onions, roughly chopped (about 1 1/2 quarts); 3 large carrots, peeled and roughly chopped (about 1 quart); 4 stalks celery, roughly chopped (about 1 quart; 12 thyme sprigs; 1 whole turkey (12 to 14 pounds total), butterflied according to these instructions, backbone, neck, and giblets reserved; 2 tablespoons vegetable oil; Kosher salt and freshly ground black pepper; 1 1/2 quarts low-sodium homemade or store-bought chicken or turkey broth; 2 bay leaves; 3 tablespoons butter; 4 tablespoons flour