Preheat oven to 250°F or warm setting. Cut your bread into 1 inch cubes (12 cups total) and spread out on a baking sheet. Place in the warm oven and bake until the cubes are dry, approximately 45 minutes. Remove from oven and set aside.
Adjust oven to 350°F. Spray a 9x13 inch baking dish with cooking spray.
In a medium pot or large skillet, cook the sausage over medium heat until cooked through. Break up sausage as needed to prevent large clumps.Place the cooked sausage in a large mixing bowl. Any fat or oil can remain in the pot/skillet.
In the same pot/skillet as the sausage fat, melt the butter over medium heat. Add the onion, celery, sage, salt, and black pepper. Simmer until the vegetables are softened, approximately 5 minutes.
Whisk the eggs to break them up. Add the eggs, stock, bread cubes, and onion sage mixture to the large bowl that the sausage is in. Toss to combine and pour into the prepared baking dish. Cover with foil.
Bake the stuffing for approximately 35-40 minutes, or until the moisture is absorbed and stuffing is setting.
Remove the foil cover and continue cooking another 15 minutes to crisp up the top. Serve warm.
If using a very soft bread like French bread, be very gentle when cutting to avoid smashing the bread and losing volume. Use a serrated knife and a gentle grasp.A dense bread is recommended as it will hold its shape better and provide more texture.This can be made up through assembly in advance and then refrigerated. Bake when ready to serve.One large loaf of French, Italian, or rustic bread is enough for this recipe. If the bread is not quite 12 cups that is fine, as long as you get to 10 cups or more.