Add 3-½ cups of the broth to a saucepan, along with the rice, and bring the broth to a boil. Reduce heat, cover and simmer for about 20 minutes, or until the rice is tender.
In a skillet, saute the onion and celery bits in butter until they're tender. Stir in the rice, mushrooms, parsley, poultry seasoning, salt, pepper and the remaining ½ cup of chicken broth. Remove the pan from the heat.
Pour the rice dressing into a greased 13x9-inch baking dish. Bake the dressing uncovered at 350°F for 30 minutes. Garnish the dressing with fresh sage and thyme, if desired.
