Melt 1/2 stick margarine in a skillet on the stove. Add 1/2 onion (chopped) and 1 stalk celery (chopped). Saute the onion and celery until the onion is clear. Remove from heat. In a large mixing bowl, combine 2 1/2 cups herb-seasoned stuffing mix and 2 1/2 cups cornbread (or cornbread stuffing mix). Add 1 teaspoon ground sage. Mix thoroughly. Add onion and celery mixture to stuffing-sage mixture, and mix all together. Now, add 2 1/2 cans chicken broth (or enough until mixture is *very* soupy. Spray an 8-inch by 12-inch Pyrex dish with cooking spray, and spoon the completed dressing into the dish. If it is not "swimming" in broth, you may add a little more over the top at this time. (Making it soupy is the key to success with the juiciness of this recipe.) Place the dish of dressing in an oven that has been preheated to 350 degrees. Bake 30 to 45 minutes, or until your desired doneness. It should be crispy around the top, but nice and juicy when you dip into it. You won't need another dressing recipe after you try this one! My (extended) family has designated me as the dressing-maker at Thanksgiving, and I am telling you my secret of success!!!