Place giblets in a pot and cover with water
Add celery stalks, yellow onion, carrot, parsley, salt and pepper.
Bring to a boil then reduce to a simmer
Cover and cook for 3-4 hours (while the turkey is cooking) and adding more water as needed to keep ingredients submerged
When the turkey is cooked, allow to rest in the roasting tray for about 10 minutes before removing. Spoon almost all the accumulated fat off the drippings
Pour turkey drippings into a pan with flour and cook for a few minutes until the flour is absorbed.
Add some of the giblet liquid and continue stirring out any lumps. Continue adding liquid until the gravy has thickened and is smooth.
The amount of turkey drippings you end up with will determine how much gravy you will get. If you need to extend the gravy you can mix additional flour and some milk to make a richer gravy.
Season with additional salt and pepper, garlic powder or salt, Worcestershire
Finely chop any of the giblets you plan to use and add to the gravy (NOT the neck).