Cut off the wing tips and put in large pot of water along with the turkey parts usually found in the turkey (neck, giblets, heart, etc). Cut the bottom 4-5 inches off the bottom of both stalks of celery and toss 'em in the pot along with the celery hearts and one of the onions (peeled and quartered). Boil for a few hours adding water if necessary, the object is a good stock. Add some fresh ground pepper.
brown sausage, drain saving the grease if there is any. chop up 1 onion
and remaining celery and saute in the grease - add butter or bacon grease
If you use a sausage that's not hot, fry it up with some Hot Hungarian Paprika.
scramble up egg in a cup or bowl with about a tsp of salt.
When you have a good turkey stock, open 1-2 bags of croutons into a bowl. Wet with one or two cups of broth. Add onions and celery (grease and all) and add sausage. Pour in egg (you want to be careful you don't start cooking it) and mix well. Add sage, if it not powder rub it real good between your hands first. Slowly add remaining croutons and add broth as necessary to keep somewhat moist (not wet). Bake in 325 oven till done.
Back to the stock. After using some of it for the stuffing, add water to bring it back up. When turkey's done, strain out what's left of the onion and stuff so you have a clean broth. Add turkey drippings (if any) and/or remaining injection liquid. Bring to good boil and thicken with corn starch/butter roug or thicken with mashed potatoes (or both). There's your gravy.