In a skillet, saute onions and celery in butter until tender. Transfer to a large bowl; add the sweet potatoes, apples, bread cubes and walnuts. Add eggs; toss to coat. Stir in the remaining ingredients. Spoon into a greased 2-1/2-qt. baking dish. Cover and bake at 350° for 40 minutes. Uncover; bake 10 minutes longer or until lightly browned. Yield: 10-12 servings.