1. Soak tamarind in 1 cup warm water.
2. Roast the spices. Cool and grind into a smooth paste adding some water.
3. Extract 2.5 cups of tamarind water.
4. Discard the tamarind.
5. Add salt, hing, sambar powder, 1 cup water and boil for 12-15 minutes.
6. Add the ground spice paste and continue boiling for another 10 minutes.
7. If the mixture is not thick enough, add rice flour paste and stir continuously for a minute.
8. Add jaggery and stir.
9. Season with mustard seeds and curry leaves.
10. Serve hot with rice and ghee.

Courtesy: http://spicesetc.blogspot.com/