Preheat the oven to 350°F, and spray an 8-inch square with cooking spray.
Add the stuffing mix, diced apple, dried cranberries, walnuts, cinnamon, and rosemary to a large, heat-safe mixing bowl. Set aside.
12 ounces herb stuffing mix, 1 large apple, 1 cup dried cranberries, ½ cup chopped walnuts, ½ teaspoon cinnamon, ½ teaspoon dried rosemary
Heat a small skillet over low-medium heat. Add 1 tablespoon of butter, celery, and onions, and cook for 4-5 minutes until softened. Add the celery and onions to the bowl with the stuffing mix, and stir to combine.
1 cup celery, 1 cup white onion
In a medium saucepan over high heat, bring the broth and remaining 3 tablespoons of butter to a boil. Remove from heat.
2 cups low-sodium chicken broth
While stirring, slowly pour the hot liquid over the ingredients into the mixing bowl. Stir until everything is coated and well hydrated. The mixture should well moist, but not overly wet or soggy.
Transfer the mixture to the prepared baking dish, and bake, uncovered, for 20-25 minutes. The top will be brown and crunchy and the center will be soft when the stuffing finishes cooking.
Top with freshly chopped parsley, and serve warm.