Wash & pressure cook toor dal along with one tomato & turmeric powder till soft. Mash it completely using back of ladle or blend it to smooth paste.
Cut another tomato into small pieces.
Soak tamarind in hot water & extract thick juice & discard the pulp.
Method
In heavy bottom vessel, take cooked dal tomato mixture, cut tomato pieces, tamarind extract, slit green chillies, jaggery & salt.
Add required water to bring the saaru to desired consistency. Cook this till tomatoes are soft (approx. 5-7 minutes).
Then add in about 2 tsp of rasam powder & bring it to boil.
Add coriander leaves & greed coconut. Switch off the flame.
Lastly heat coconut oil/ghee in tadka pan, add mustard seeds. Once they splutter, add curry leaves, dry red chillies & hing. Pour this over prepared saaru/rasam & mix well.
Udupi style Saaru or Rasam is ready to serve with steaming hot rice.