Boil water in a pan. Make a paste of rasam mix with a little water and add to the boiling water. Keep it on a slow fire. Chop finely small onion and garlic. Add to Rasam. Add salt to taste. Heat oil in a frying pan, Add Mustard seeds and let it splutter. Add sliced small onions, broken red chillies and curry leaves. Pour this to the rasam. Serve hot garnished with finely chopped corriander leaves.

N.B. : lime juice or chopped tomatoes can be added for more sourness.