Wash and chop the tomatoes into big chunks. Grind it to a fine puree.
Take a lemon sized tamarind, add little water and boil it to extract tamarind juice. Keep it aside.
In a pan, add ghee, splutter mustard seeds. Once they crack add cumin and saute for a minute.
Then add curry leaves and saute.
Add tomato puree into the pan. Also add tamarind juice into the pan.
Add required amount of salt, turmeric powder, rasam powder, jaggery, asafoetida, pepper-cumin powder.
Add water to adjust the consistency of the rasam. Allow it to boil.
Once the froth starts appearing, turn off the stove and garnish it with fresh coriander leaves.
Serve it with hot rice, fryums and some poriyal.