Preheat the oven to 350 degrees F (175 degrees C). Combine the onion, green pepper, celery and garlic in the container of a food processor or blender. Process until finely chopped. Stir in 1 tablespoon of the Creole seasoning.
Cut about 8 slits across the roast about 1/2 inch deep. Pack the vegetable mixture into the slits. Rub the remaining tablespoon of Creole seasoning all over the roast. Coat the roast generously with bacon grease, and place in a roasting pan.
Bake uncovered for 1 hour, until browned, then cover, and continue cooking for about 3 more hours, or until tender. After the roast is done, you can skim off some of the excess fat and thicken the drippings with a mixture of water and flour if you want your gravy thicker.