Preheat the oven to 350°. After turkey has thawed, remove the neck and giblets from the inside of the body cavity. Wash them in cold water and pat dry with paper towels and set aside. Rub the turkey skin with oil and sprinkle with salt and pepper to taste.
Rub the cavity of the turkey with 1/4 lb. of butter, and season with additional salt and pepper. Stuff the turkey with two of the chopped carrots, 2 stalks celery, 1 onion, 5 garlic cloves, 5 sprigs Italian parsley, rosemary and 3 sprigs thyme.
Place turkey in a baking pan, and put into the oven for 2 to 3 hours. The rule of thumb is 13 minutes per pound, however it’s best to use a thermometer to monitor doneness. The turkey is fully cooked when the internal temperature reaches 160°.
While the turkey is roasting, make the gravy. Place the neck and giblets in a large pot on medium low heat; slowly brown until fully cooked, about 5 to 10 minutes. Add the remaining chopped onion, carrots and celery and continue to slowly brown the veggies. Add the 4 sprigs thyme, 4 sprigs Italian parsley and stock to the large pot. Simmer for 1 hour.
Once the turkey is fully cooked, remove from the oven. Strain the fatty oils from the roasting pan, keeping “fond” or crisp, browned vegetable pieces stuck to the pan along with the strained stock.
Next, make a roux to thicken the gravy. Melt ½ lb. butter in a small pot over medium low heat. Add the flour and whisk continuously 5 minutes until you have a smooth paste. Set aside.
Pour the reserved stock back into the large pot and whisk in the roux, to thicken and finish the gravy. Reduce by one-third over medium-high heat for about 20 to 30 minutes. Season with salt and pepper, to taste.