Soak all four spice paste ingredients in scalding hot water for about 20 minutes until soft. Grind to a fine paste with as little water as possible. Set aside.
Combine the water, tamarind, tomatoes, asafetida, turmeric and salt with the water and bring to a boil. When the tomato has cooked down, add the torn curry leaves along with the spice paste. Allow to simmer until the spices appear to have lost the raw smell. Remove from the stove top.
Heat the ghee in a small skillet until it just begins to smoke. Toss in the cumin and allow the seeds to split. Pour the sizzling mixture over the rasam. Garnish with coriander leaves prior to serving.
Notes
• The amount of tamarind extract depends on the sourness and tartness of the tomatoes. If the tomatoes are not too sour, increase the quantity of the tamarind extract till the desired taste is achieved. • Fresh red chillies are recommended but if not available, dry red chillies can also be used.