Blanch tomatoes, this is optional but it renders beautiful red colour to rasam. Ground tomatoes to smooth puree
Grind coriander leaves, garlic, ginger, cumin seeds, pepper to coarse paste
Heat oil or ghee in a pan
Splutter mustard seeds
Add Urad dal and saute until golden brown
Add curry leaves, red chillies and ground paste
Saute for few seconds. Add turmeric and mix well over low heat
Saute until aromatic. Add tomato puree and mix well
Add salt and cook for 1 min
Add water and mix well. Bring to boil
Simmer cover and cook for 8-10 minutes. Switch off
Add 2 tbsp chopped coriander leaves and mix well
Serve hot with rice