1. Blend the tomatoes to a smooth puree in a blender. Do not add any water while blending.
2. Boil the tomato puree on stove for about 4-5 mins. Add the rasam powder and boil further for another 4-5 mins.
3. Add water if you feel the puree is very thick.
4. Add salt, jaggery and mix well.
5. You can even add a couple of spoons of grated coconut and chopped cilantro.
6. Since the tomato already has a sour taste, you need not add any tamarind.
7. Temper with mustard seeds, jeera, hing and curry leaves; Serve hot with rice.

Courtesy: http://maneadige.blogspot.com/