Boil celery and onions in water until the celery is soft. Drain and set aside. Brown meat in frying pan and drain. Cook elbow macaroni as per directions on box. Mix all together in pot. In a greased casserole dish alternate layers of meat mixture and Velveeta slices, repeat layers with the last one being of Velveeta slices. Bake covered at 350 degrees for 1/2 hour.