Roast Turkey in Parts Recipe

Name: Roast Turkey in Parts Recipe
Ingredients: 1 whole turkey, 10 to 15 pounds (4.5 to 6.8kg); Kosher salt and freshly ground black pepper; 1 large onion, peeled and roughly chopped (about 2 cups); 1 large carrot, peeled and roughly chopped (about 1 cup); 2 large ribs celery, roughly chopped (about 1 cup); 2 medium cloves garlic, peeled and smashed; 2 bay leaves; 12 whole black peppercorns; 1 quart (900ml) homemade or store-bought low-sodium chicken stock, divided; 2 tablespoons (30ml) vegetable oil; 3 tablespoons (45g) unsalted butter; 3 tablespoons flour; 1/4 teaspoon marmite; 1 teaspoon (5ml) soy sauce