Onion sambar is made of the shallot variety of onions, which originated somewhere between Central and Southwest Asia. Onion sambar, however, is a popular and tasty South Indian dish, served with rice and is popular because of its hot, spicy and tangy flavor. While making onion sambar at home, make sure to use shallots, which are slightly pink and elongated in shape, rather than round. Often teamed with plain rice, dosas or Idly, onion samar is one of the most common gravies prepared in South Indian households.