Soak tamarind in warm water for at least ten minutes and extract the juice. Strain the juice and set aside. Discard the fibre.
In a mixer grinder, add cumin seeds, pepper , curry leaves , garlic cloves, and tomato and grind them together into a coarse paste.
In a pan add the tamarind extract, ground tomato paste , rasam powder, turmeric powder , a small piece of jaggery, water and salt. Mix it well.
Add the required amount of water to adjust the consistency of the rasam.
Add chopped coriander leaves over it.
Bring this rasam to a gentle boil . Once you see the bubbles on the top of the rasam, switch off the stove. Do not overboil the rasam, as it reduces its flavour.
Heat oil in a small pan. Add mustard seeds and allow them to crackle. Next, add urad dal , curry leaves , asafoetida, and fenugreek seeds and sauté them.
Pour this tempering over the rasam.
Serve this rasam hot with steamed rice and poriyal.