In a large mixing bowl, toss together the crumbled cornbread and bread. Add the salt, pepper and poultry seasoning; set aside.
Saute the onion and celery in butter or olive oil til just tender. Add the sauteed vegetables to the mixing bowl and toss together til combined.
Add 1/2 cup chicken bone broth and stir to combine. Add more broth in 1/4 cup intervals, as needed, until mixture starts clumping together - can hold a shape.
Spoon the bread mixture into a greased or sprayed 9"x9" baking dish.
Press pieces of roast chicken into the top of the dressing. Slowly pour more chicken broth over top until mixture is quite wet - but not soupy.
Bake at 400 degrees for 40-45 minutes or until top is golden in color, and dressing is set. Dressing will continue to thicken slightly as it sits/cools. Serve warm. See notes below if your dressing is not firm enough.