Soak tamarind in water for 30 minutes or you can soak it in warm water for 15 minutes. Extract around 3 cups of tamarind water, about 750 ml
Take the ingredients given under To Grind , in a mixer or use a mortar-pestle to grind to a coarse powder. This is our rasam powder
Take tomato, garlic, ginger, garlic,green chili,coriander into a mixer of chopper and grind it coarsely. You can use mortar and pestle too, if you are comfortable. Few mint leaves can also be added for flavor
Take the tamarind water in a heavy bottom pan/eeya chombu/tin vessel, add turmeric powder, hing and the ground tomato mixture
Add the freshly made rasam powder and salt to this and let it come to a boil. Once the rawness of the rasam powder disappears, which will take around 10-12 minutes, add 1/2 cup of water to the rasam.
Let the rasam froth well. Take it off the stove. Now let us do the tadka, in a tadka pan, heat oil/ghee, splutter mustard seeds, cumin and curry leaves. Pour this sizzling tadka over the rasam.
Garnish the rasam with fresh coriander leaves and serve it warm with rice.