Preheat your oven to 350 degrees Fahrenheit (175°C). Grease a 9x13-inch baking dish.
In a large skillet over medium heat, melt the butter. Add the diced onions and celery. Sauté until they become soft and translucent, about 5-7 minutes.
In the same skillet, add the Italian sausage, breaking it into small pieces with a spatula or spoon. Cook until it's browned and fully cooked, breaking it up further as needed. This should take about 8-10 minutes.
Optional: deglaze the pan with the white wine and cook until the liquid has reduced by half. .
Combine the dried bread cubes, cooked sausage, sautéed onions and celery, chopped parsley, thyme, fennel, salt, and black pepper in a large mixing bowl. Mix everything together until well combined.
Slowly pour the chicken broth over the mixture. The amount of broth you need may vary depending on how dry your bread cubes are. Start with 2 cups and gradually add more until the mixture is moist but not overly wet. You want the stuffing to hold its shape. Allow time for the mixture to absorb the broth before adding more.