Soak a small lemon sized tamarind firstly in half cup hot water for 15 mins minimum or upto 30 mins.
After that, extract the tamarind juice to make it 1 cup in total (use another ½ cup to extract the pulp). Set aside.
Next, add roughly chopped tomato to the tamarind juice and crush your hands to soften it, bringing out the pulp. Set aside.
Meanwhile, gather the ingredients needed to crush.
Now, take a mortar pestle and add the ingredients for crushing along with rock salt. Rock salt helps crushing easily, however, if you don't have just use table salt.
Rock salt, ½ tsp Black Pepper, ½ tsp Cumin seeds, 2 Green chillies, 7 cloves Garlic , ¼ cup Coriander leaves
Crush furthermore until you get a coarse paste.
Add it to the tamarind juice.
Meanwhile boil 2 cups water.
Pour it to the rasam.
Add jaggery and mix furthermore.
Taste and adjust the salt if needed. It should be slightly more as when you mix with hot rice, it will be balanced.