Preheat the oven to 300 degrees. Place the bread in a single layer on a baking sheet. Bake for 20 minutes or until the bread is fairly dry. Remove from the oven and place in a 9 x 13 inch baking dish.
Remove the casing from the sausage and cook in a skillet over medium high heat. Heat until browned, stirring to crumble. Remove from the pan and place in a large bowl.
Increase the oven temperature to 350 degrees.
Heat the oil in the same skillet over medium heat. Add in the onion, garlic, celery, and mushrooms. Cook for 10 minutes or until the vegetables are tender. Remove from heat and stir in the sage, rosemary, salt, and black pepper.
Add the onion mixture to the sausage and mix well. Stir in the chicken broth and mix well to combine.
Pour the onion and sausage mixture into the pan with the bread and mix well.
Cover and bake for 15 minutes. Remove the foil and continue baking for 20-25 minutes or until the top is crispy.