Soak tamarind in warm water for 10-15 minutes and extract tamarind water, discarding the pulp
In a heavy bottomed pan, add oil and let it heat. Once when the oil is hot add the ingredients under to temper and let it crackle
Add onion and green chilli saute till onion is translucent
Add sambar powder and give a quick stir
Add the tamarind extract, salt and let it boil for 18 - 20 minutes on medium flame, stirring occasionally
Add jaggery and let it melt and cook for another 2-3 minutes. Switch off