Preheat your oven to 350°F (175°C). Spread the cubed 12 cups sourdough bread on a baking sheet and toast for 10-15 minutes until lightly golden and crisp. Set aside.
12 cups sourdough bread
Heat 2 tbsp unsalted butter in a large skillet over medium heat. Add the sliced 2 medium onions and a pinch of salt. Cook, stirring occasionally, until the onions are golden brown and caramelized, about 25 minutes. Remove from the skillet and set aside.
2 tbsp unsalted butter, 2 medium onions
In the same skillet, add the 1 lb sweet Italian sausage. Cook over medium heat, breaking it into crumbles, until browned and fully cooked. Add the 3 celery stalks and 2 garlic cloves, cooking for 3-5 minutes until softened.
1 lb sweet Italian sausage, 3 celery stalks, 2 garlic cloves
Add the 2 tsp fresh thyme , 2 tsp fresh sage, 2 tsp fresh rosemary, 1 tsp salt, and 1 tsp black pepper. Stir to combine and cook on low heat for 2-4 more minutes.
In a large mixing bowl, combine the toasted bread, caramelized onions, sausage mixture, fresh herbs, salt, and pepper. Pour in the 1 1/2 cups chicken broth and 1 egg, stirring until the bread is evenly moistened. Add more broth if the mixture seems dry.
2 tsp fresh thyme , 2 tsp fresh sage, 2 tsp fresh rosemary, 1 tsp salt, 1 tsp black pepper, 1 1/2 cups chicken broth, 1 egg
Transfer the stuffing to a greased 9x13-inch baking dish. Cover with foil and bake at 375°F (190°C) for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, until the top is golden and slightly crisp.
Let the stuffing rest for 5 minutes before serving. Garnish with additional fresh herbs if desired.