Dry the bread (if needed): Spread sourdough cubes on sheet pans and bake at 300°F for 10–15 minutes until dry to the touch (sourdough can dry a bit faster). Cool. Increase oven to 375°F and spray a 9×13-inch dish with cooking spray.
20 ounces Sourdough Bread
In a large skillet over medium heat, cook ground sausage until mostly browned, 5–6 minutes. Add onion and celery and continue cooking until the sausage is fully cooked and the veggies are softened, 3–4 minutes more. Transfer the sausage mixture to a paper-towel-lined plate or tray to drain off excess grease.
1 pound Ground Sage Pork Sausage, 1 Small Onion, 1 cup Celery
Add sourdough cubes, drained sausage, sautéed onion/celery, and parsley to a very large bowl.
2 Tablespoon Fresh Parsley
In a separate bowl or large measuring cup, whisk together eggs, chicken broth, sage, thyme, marjoram, rosemary, nutmeg, black pepper and kosher salt.
2 Eggs, 3 cups Chicken Broth, 2 teaspoon Dried Sage, 1 teaspoon Dried Thyme, 1 teaspoon Black Pepper, ¾ teaspoon Dried Marjoram, 1 teaspoon Dried Rosemary, ¾ teaspoon Ground Nutmeg, 1 teaspoon Kosher Salt
Pour the whisked liquid evenly over the bread mixture. Toss gently until every cube is moistened; add up to ½ cup more broth if needed. The mixture should hold together when pressed but not be soupy.
Transfer to the prepared dish. Cover tightly with foil and bake for 30 minutes at 375°F. Remove foil and bake 15 minutes more, until the top is lightly golden and the center reads 165°F.
Let stand 5–10 minutes before serving.