Cut the cornbread into cubes and dry on a sheet tray at 250 F for about 3 hours. Stir it once or twice to make sure all of the cubes are dry.
When the cubes are dry saute the onion and celery in your fat of choice for 5 minutes or so. Add the dried sage, salt, and pepper.
Put the cornbread cubes back into the 9 x 13 you baked the cornbread in and mix with the onion and celery mixture. Use the turkey broth to add more moisture to the cubes. The cubes should be moist, no longer hard, but not soggy. Adjust the amount of broth to suit your taste.
Pro Tip: Make this a day before you need it and pop it in the refrigerator to let the flavors marry.
Cover with aluminum foil and bake at 350 F for 30-40 minutes. Check the moisture level about half way through the cooking process. If it is too dry add a bit more broth and re-cover with foil; if it's too wet remove the foil and allow it to bake uncovered. If it is fine, continue to keep it covered. If you'd like some drier bits on top, remove the foil after the 30 minute mark, and bake uncovered for 15-20 minutes.
This is the turkey broth that I use:
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