Cut day-old bread into roughly 1-inch cubes. Spread on a baking sheet and toast in a 300°F (150°C) oven for about 15-20 minutes until dry and slightly golden. Remove and set aside.
Heat olive oil in a large skillet over medium heat. Add ground chicken sausage and cook, breaking it up with a wooden spoon, until browned and cooked through, about 6-8 minutes. Remove sausage from skillet and set aside, leaving drippings in pan.
Add butter to the same skillet. Once melted, add chopped onion, celery, and garlic. Cook until softened and fragrant, about 5 minutes. Then add diced apples and cook for another 3-4 minutes until apples soften but retain some texture.
Return cooked sausage to skillet and stir in fresh herbs, salt, and pepper. Add toasted bread cubes and gently toss everything together.
Slowly pour in chicken broth while stirring, until bread is moist but not soggy. Add broth gradually to reach desired consistency.
Transfer mixture to a greased 9x13-inch baking dish. Cover with foil and bake at 350°F (175°C) for 25 minutes. Remove foil and bake an additional 15 minutes until top is golden and slightly crispy.
Allow stuffing to cool for a few minutes before serving. Pairs well with roasted chicken, turkey, or can be made vegetarian by omitting sausage and using vegetable broth.