Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish and set it aside.
Cut the focaccia bread into 1-inch cubes and spread them out on a baking sheet. Toast them in the preheated oven for about 10-15 minutes, or until they're slightly dried out and crispy. Remove from the oven and let cool.
In a large skillet, heat the olive oil over medium heat. Add the Italian sausage and cook, breaking it up with a spoon, until it's browned and cooked through, about 8-10 minutes.
Add the diced onion and celery to the skillet with the sausage. Cook for another 5 minutes, or until the vegetables are softened.
Stir in the minced garlic, dried sage, thyme, rosemary, salt, and pepper. Cook for another 2 minutes, until the garlic is fragrant.
Transfer the toasted focaccia cubes to a large mixing bowl. Add the sausage and vegetable mixture, along with the chopped parsley. Toss everything together until well combined.
Pour the chicken or vegetable broth over the mixture and toss again until the bread is evenly moistened. If you prefer a moister stuffing, you can add more broth as needed.
Transfer the stuffing mixture to the prepared baking dish, spreading it out evenly.Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Then, remove the foil and bake for an additional 15-20 minutes, or until the top is golden brown and crispy.
Once done, remove from the oven and let the stuffing cool for a few minutes before serving. Enjoy your delicious Focaccia Stuffing with Italian Sausage!