Preheat the oven to 250 degrees F.
Cut the bread into 1/2" to 3/4" pieces and lay them in a single layer on baking sheets.
Bake in the preheated oven for about 1 hour, tossing a few times to make sure all sides are dry. Once dried, remove from the oven and transfer to a large bowl. Set aside while you make the rest of the stuffing.
Increase oven temperature to 350 degrees F.
Put butter to a large pot over medium heat and melt. Add the celery and onions and cook, stirring frequently, until tender and translucent—about 8 minutes.
Add the sausage and use the bottom of the spoon to break the sausage up into small chunks. Cook the mixture until the sausage is no longer pink, then add the diced apples and cook for an additional minute. Finally, add the poultry seasoning, minced parsley, thyme, sage, salt, and pepper.
Add 2 cups of broth to the sausage mixture and pour it over the bread. Fold gently, adding more broth ½ cup at a time until the bread is evenly moist with no standing liquid.
Spray a deep 9x13-inch dish, a 10x15-inch pan, or two 8x8 pans, with nonstick cooking spray, then spread the bread mixture evenly over the bottom.
Bake in the preheated oven for 45-60 minutes, stirring gently every 15 minutes, or until the top is lightly brown.
Remove from the oven and serve warm. Enjoy!