In a large stock pot cover chicken and onion with water. Cook slowly until tender, approximately 1 hour. Remove chicken, let cool and remove meat from bones. Cut meat into 1 inch pieces, discard skin and bones.
Cut corn from cobs if using fresh corn.
Add corn, cut up chicken, celery to stock pot and season with salt and pepper. Simmer soup for 10 minutes.
In a separate bowl make rivels by mixing together flour, salt, egg, and enough milk to form small crumbs.
Drop rivels into soup and add hard boiled eggs. Simmer for 15 minutes and serve hot.