Preheat oven to 350 F. Coat a 3 quart casserole dish with 1 tablespoon butter and set aside. Melt remaining butter in a large saucepan over medium high heat. Add the mushrooms and saute for 10 minutes. Add the celery and onion and saute for 10 minutes. Remove from heat, add the remaining ingredients and toss to combine. Transfer the stuffing to the prepared baking dish and cover with aluminum foil. Bake, covered, for 45 minutes, remove the foil and bake for 20 more minutes. Serve hot.