Turn Ninja to Stovetop-High. Put butter & olive oil in Ninja. Once butter is bubbling put celery and onions in. Saute until celery is translucent.
If you are not using sausage or mushrooms, mix the bag of stuffing with the celery and onions.
If you are using sausage and mushrooms, mix the sausage, mushrooms and stuffing with the celery & onions.
Pour the chicken broth into the mix.
Switch the Ninja to oven. Set to 250 degrees for 25 minutes.
DONE!