Before starting, make sure you soak tamarind and extract juice (total ½ cup).
Keep ready dal water (½ cup) - You can cook ¼ cup dal and prepare ½ cup water from it or save it from dal you cook for sambar.
Take eeya sombu (or any other vessel) and add tamarind water to it.
After that, add chopped tomato reserving a little for topping.
Smash the tomato well with hands.
Take ½ cup loosely packed mint leaves with little water.
Add the ground mint to rasam.
Add turmeric, rasam powder, asafoetida and slit chilli to it.
Add 1 cup water.
Start heating in low heat. Do not use high flame while using eeya sombu.
Once it froths, add dal water.
Top with remaining tomato.
Bring to boil again in low to medium flame. Just until it froths. Remove from fire.
Heat a teaspoon of ghee, temper with mustard, asafoetida and cumin seeds.
Mix the tempering to rasam.
Garnish with some fresh mint leaves, finely chopped.