Preheat the oven to 350 degrees, although you can also just add the extra stuffing in your baking dish to your hot oven while the turkey is roasting for the last hour. Grease a medium size baking dish with half the butter stick. Melt the other half of the butter in a large sauce pan under medium heat. Sautee chopped onion and celery, stirring until they are soft. Add sausage to the pan and sauté, breaking up the meat with your spoon or a fork until no longer pink. Add apple, sage, salt and pepper, and mix everything together, cooking for a few minutes longer. Turn off stove and let mixture cool for 5 to 10 minutes. Meanwhile, beat egg and milk or water in a large bowl big enough to hold all the stuffing. Add the chicken broth and mix together well. Then add the stuffing and the sausage mixture and blend all the ingredients together well. If you’re stuffing your turkey, which we always do, carefully spoon some of the stuffing mixture into the cavity. Don’t pack it too tightly, and when you’ve finished, try to close up the opening as best you can (a piece of string or skewer is also helpful). Spoon the remainder into the buttered baking dish, cover with aluminum foil and place in the fridge until an hour and a half before the turkey is finished cooking. The extra stuffing will take about one hour to cook with the turkey at 350 degrees. Remove the foil for the last 15 minutes to brown the stuffing. Serve piping hot in the baking dish but remember to put place mats under the hot dishes or platters if you have a wood surface.