Pressure cook green gram with enough water till it turns soft. I cooked it for 3 whistles and 5 minutes in simmer. Once cooked, let it cool down to room temperature and mash it or blend it using blender.
Method
Chop the tomatoes to fine cubes and slit green chillies. Also soak tamarind in 1/4 cup water for about 10 minutes. Next heat a cooking pan with oil. As oil gets heated up add mustard seeds, red chilly and cumin. As they crackle include curry leaves and saute.
Next throw in chopped tomatoes, slit green chillies and turmeric powder. Continue sauteing till tomatoes get cooked. Then include tamarind extract discarding the residue. Let it boil for few minutes.
Next add jaggery and mashed green gram along with enough water. Let the rasam boil.
Finally add salt, rasam powder, asafoetida and bring it boil for few more minutes. Garnish with coriander leaves.
Notes
Balance the tamarind and jaggery quantity for the authentic rasam taste.
I have used Udupi rasam powder, you can use either home made or store bought one.
Be generous with coriander leaves that enhances the taste of rasam.