add ⅓ cup (about a handful) of roughly chopped coriander stems, with or without leaves. Add 7 to 8 medium sized garlic cloves, peeled, and 1 inch of peeled ginger, roughly chopped.
Add 2 teaspoons of cumin seeds and ¼ teaspoon of whole black peppercorns
Grind to a coarse paste, but do not puree. Transfer the paste to a bowl or plate and set aside.
To the same blender jar add 3 large ripe and red tomatoes, rinsed and chopped. You will need 275 grams tomatoes, or roughly 1.5 to 1.75 cups of chopped tomatoes.. Blend the tomatoes until smooth.
In a pan, heat oil. Once the oil is hot add ½ teaspoon of mustard seeds. Fry the seeds until the begin to crackle.
Next add ½ teaspoon of urad dal (lentils). I have used whole urad dal, but you can even use split and husked lentils. Continue to stir often as you fry the urad dal to a golden brown.
Add 1 to 2 dry red chilies (halved and seeds removed), and 1 pinch asafoetida (hing). Turn the heat off if the pot gets too hot. Fry the chillies for a few seconds.
Add the coarsely ground coriander, ginger, cumin, black pepper and garlic paste to the pan. Again, if the pan is so hot that anything begins to burn, promptly turn the heat off. Now add 10 to 12 curry leaves, whole or chopped.
Sauté for a minute, then add ¼ teaspoon of turmeric powder.
Stir the ingredients. Carefully, add the tomato puree. Mix well. Continue to stir and simmer.
Season with salt according to your preference. Next add 1.5 cups of water, and stir. If you want a thinner soup you can add a splash more water. Bring the mixture to a gentle boil. Turn the heat back down and simmer for 10 minutes.
. Turn off the heat and add 2 tablespoons of chopped coriander (cilantro) leaves. Taste, and add more salt if needed. Serve tomato rasam or thakkali rasam hot, either like a curry over steamed white rice or enjoy as a bowl of hearty soup.