In a saucepan, boil potatoes; drain & mash. Set aside. Saute onion, celery, garlic, mushrooms & seasonings in margarine. Remove from heat. Combine with bread cubes, mashed potatoes & broth. ADD ONLY ENOUGH BROTH TO MAKE A PROPER STUFFING CONSISTENCY. You may not need the full amount of broth. This will make sufficient stuffing for a 4 – 4.5 kg (9 – 10 lb) turkey.