Heat oven to 325º. Grease bottom and side of 3-quart casserole or rectangular baking dish, 13x9x2 inches, with shortening.
Melt butter in 4-quart Dutch oven over medium-high heat. Cook celery and onion in butter, stirring occasionally, until tender; remove from heat.
Toss celery mixture and remaining ingredients. Spoon into casserole.
Cover and bake 30 minutes. Uncover and bake about 15 minutes longer or until heated through.