Preheat your oven to 350°F (175°C).
In a pan, melt the margarine or butter over medium heat.
Add the chopped celery and onion to the pan and cook them until they become soft.
In a large bowl, mix together the cooked celery and onion with the crumbled cornbread.
Pour in the chicken broth and beaten egg.
Add the poultry seasoning, ground sage, salt, and black pepper to the bowl.
Gently toss everything together until the bread is evenly moistened by the other ingredients.
Take an 8-inch square baking dish or a 1 1/2-quart casserole dish.
Transfer the mixture to the baking dish, spreading it out evenly.
Put the baking dish in the preheated oven.
Bake for around 40 to 45 minutes, or until the dressing is heated through and gets a little crispy on top.
Alternatively, you can use this dressing to stuff a 12-pound turkey. If you choose this method, follow the regular roasting instructions for the turkey.