Wash the toor dal ,add turmeric and cook for 3 - 4 whistles with 2 cup of water. Mash the cooked dal and keep aside.
You can use tomatoes in 2 ways. Either cook tomatoes in cooker , mash them and boil it with slitted green chilli . or Chop tomatoes and boil it directly in a vessel along with green chilli .
When the tomatoes are cooked , mash them lightly . To that add salt , squeezed tamarind pulp , jaggery , rasam powder and cooked tuvar dal. Add water to get desired consistency .
Let it boil nicely on sim till a bit frothy. Garnish with chopped coriander leaves ,curry leaves and grated coconut . Switch off .
Finally prepare a tempering. Take a small kadai or pan . Add coconut oil or ghee. When its hot add mustard seeds. When it splutters add jeera and hing. Switch off .Pour the tempering on the hot rasam and close the lid. Allow it to sit for some time so the aroma of the tempering infuses in the rasam . .
Serve hot tomato rasam with hot rice drizzled with ghee .