Wash tomatoes nicely.
In pan boil tomatoes till the skin splits.
Take out off heat, transfer to cold water.
Peel the skin and roughly chop the tomatoes or grind to smooth puree. Keep aside.
In grinder, add coriander leaves, ginger, garlic and green chilies. Grind to coarse paste.
In a pan heat oil. Add mustard seeds, when it crackles add urad dal.
Once the lentils/dal starts to turns light brown.
Add coarse coriander paste, sauté till the raw smell of garlic goes way.
Add tomato puree and cook for few minutes.
Add water till it boils nicely.
Add black pepper powder and salt as per taste.
Add jaggery to balance the acidity of tomatoes.
Add finely chopped coriander leaves and stems.
Serve hot rasam with papads or rice.