Leave diced bread out on a counter over night to stale up. Preheat oven to 375°F. Alternatively, you could spread bread on baking pan and bake until toasted, about 5-8 minutes while you prepare the other ingredients.
In a large nonstick skillet sauté sausage, breaking it up with a wooden spoon as it cooks. Drain meal on a plate with paper towels and return to skillet. Stir in celery, onion and apple and sauté until just tender, about 8 minutes. Add 1 cup of broth, stirring and scrapping bottom to release all of those yummy browned bits, about 1 minute.
In a very large bowl, stir together bread cubes, sausage/veggie mixture, sage, thyme, salt, and pepper.
In a small bowl, whisk remaining 1/2 cup of broth with the 3 eggs. Stir into bread mixture.
Spoon stuffing into a 9 x 13-inch casserole dish, cover with tin foil, and bake for 15 minutes. Remove tin foil and continue baking until browned on top, about 15-20 minutes. Cut into 8 pieces and serve.