Wash tamarind and then soak in 1/2 cup warm water and then after an hour squeeze out the juice,strain and keep side.
Add cumin,pepper corn and whole red chili in the mixer jar and grind to make a powder.
In a pan add the finely chopped tomatoes, the tamarind extract, ground pepper cumin mix, turmeric, salt and 2 tbsp of chopped coriander and simmer for about 10 minutes or till tomatoes become soft and mushy.
Remove the froth from the boiling rasam. You can add some more water to adjust the consistency
Heat ghee in a small pan and add mustard seeds, cumin and when they start to crackle then add asafoetida and curry leaves .
Now add the tempering on the simmering rasam and add the remaining chopped coriander and switch off the flame.
Serve hot rasam with some ghee rice , raw banana fry papad and pickle