Grind garlic, black peppercorns and cumin seeds to a fine powder.
To this, add chopped tomatoes. Grind to a paste.
Transfer this paste to a cooking pot. Boil on high heat.
Add salt, turmeric powder, rasam powder, and chopped coriander leaves.
Add water. Boil on high heat for about 5 minutes.
If you like your rasam sour, add tamarind, or else skip it.
For the tempering, heat oil in a pan.
Add cumin seeds, curry leaves, dry red chillies, and asafoetida.
Fry this mixture for about 5-10 seconds on medium heat.
Put this tempering on the cooked rasam. Boil rasam for another minute. Turn off the heat and serve it hot with steamed rice and any side dish.