Cool the cornbread and crumble. Place the cornbread in a large bowl with the bread cubes and toss to combine.
Preheat the oven to 350 degrees. Coat a 9"x13" pan with cooking spray.
Melt 4 tablespoons of butter in a large pan over medium heat. Add the onion and celery and cook for 6-8 minutes or until softened. Season the vegetables with salt and pepper to taste. Place the vegetables in the bowl with the cornbread mixture.
Melt the remaining 6 tablespoons of butter and pour into a large bowl. Add the chicken broth, eggs, salt and pepper to taste, and sage and whisk to combine.
Pour the butter mixture into the bowl with the cornbread mixture and stir to combine.
Transfer the stuffing mixture to the prepared pan. Bake for 45 minutes or until dressing is browned and cooked through.
Sprinkle with parsley and garnish with sage leaves if desired. Serve.