In a large skillet, heat the butter. Add the celery and onion and sauté until softened, about 12 minutes. Transfer to a bowl and let cool.
In a large bowl, toss together the cornbread and white bread. Drizzle in the broth, tossing lightly; use just enough broth to make the mixture very moist, but not soggy. (Make sure the liquid is cool, or the stuffing mixture will become glumpy.) Add the salt, pepper, sage, and rosemary. Taste, and adjust the seasonings according to your own taste.
Stuff the turkey. Or spoon the stuffing into a buttered 13 x 9 x 3-inch baking dish, drizzle the stuffing with about ½ cup of the broth, and then cover the dish with aluminum foil and bake in a 350º oven for 1 hour. For a crispy top, uncover for the last 15 minutes.