In a small saucepan, saute onion and celery in butter until tender. Combine flour and broth until smooth; stir into the pan. Add the milk, bay leaf, onion salt and pepper. Bring to a boil; cook and stir for 2 minutes or until thickened. Remove from the heat. Discard bay leaf. Whisk in the sour cream, parsley and lemon juice.
Place the spaghetti in a greased 11-in. x 7-in. baking dish; top with pork and white sauce. Sprinkle with bread crumbs. Bake, uncovered, at 350° for 30-35 minutes or until bubbly. Let stand for 5 minutes before serving. Yield: 4 servings.