Pour the chicken broth in a pot and bring to a simmer. Or if you are using the neck and giblets from a turkey, place 6 cups of water and the neck of the turkey in a pot and simmer for 30 minutes.
Bring a large saucepan to medium heat. Add the butter or olive oil. Once hot, stir in the chopped celery and onion. Saute until soft about 8 minutes. Then add in the garlic, poultry seasoning, and salt. Saute for 1 more minute. Stir in the mushrooms until they release their water.
Remove the sausage from the casing and add it to the pan. Break it apart with a wooden spoon into the smallest pieces possible. Brown it all the way through.
Preheat the oven to 375 ℉. Add a cup of stuffing to the mixture along with a cup of broth. Stir and combine until all of the broth is absorbed. Repeat this process, adding a cup of stuffing and broth together, until you use all of the broth and all of the stuffing.
Once the stuffing comes together and the cubed stuffing is starting to mash together, remove the saucepan from the heat. Place the stuffing into a 9x13 baking dish. Spread it out evenly and place it in the oven for 30 minutes. Remove and serve.
