While the turkey is in the oven, put the turkey parts (neck and giblets) into a large saucepan. Add the stock, wine, onion, carrot and celery. Bring it all to a boil.
Reduce the heat to low and skim off any fat. Simmer for 3 hours. Strain the mixture into a large measuring cup, adding wine, if needed, to make 3 cups. Set aside.
To make the turkey gravy take 3 cups of the stock you just made above.
Put the roasting pan on the stove element. Skim off the excess fat in the roasting pan. Cook the remaining juices for 1 minute. Whisk in 2 1/2 cups of the stock, leaving out 1/2 cup, and bring to a boil, stirring to scrape up the brown bits from the pan.
Mix the 1/2 cup of the reserved stock with the flour until there are no lumps in the mixture. Add the flour mixture into the pan and immediately stir well with a whisk to make sure you have no lumps. Reduce the heat and simmer for 5 minutes, stirring often. Whisk in butter, salt and pepper to taste. Strain if desired or if it is lumpy.