In another pan heat oil.
Add the mustard seeds and urad dal.
Fry till the mustard seeds are crackling and the urad dal becomes golden.
Lower the flame and add the chopped garlic cloves, curry leaves and dry red chillies and fry for few seconds.
Now add the tomato puree and cook till the raw smell of the tomato goes away.
Add the turmeric power and asafoetida.
Stir and add the roasted ground Rasam powder.
Stir quickly and add 1 tomato cut in 4 halves to this mixture.
Now add the dal and tamarind pulp to this. Mix well.
Simmer for 8 to 10 minutes or till you see frothy layer on top on a low or medium flame. The raw aroma of the tamarind also has to go away.
Garnish the Rasam with bunch of coriander leaves and serve hot with steamed rice.