In a heavy bottom vessel in which you are going to prepare the rasam, add the tamarind paste, salt, chopped tomatoes, crushed garlic, turmeric powder, half of the curry leaves, kollu rasam powder, and fresh ground pepper.
Add 2 cups of water and mix well.
Now simmer the rasam over medium-low heat. When the rasam mix comes to a boil, add the remaining curry leaves and 2 tbsp chopped cilantro. Simmer again for a minute.
Next, add two more cups of water, reduce the heat to low, and let the rasam simmer.
When it becomes frothy, turn off the heat.
Finally, add 1 tbsp of cilantro and close the rasam pan with a lid to steep in the flavors.
Heat a separate pan or kadai or tadka pan and add ghee. When it's hot, add mustard seeds and cumin seeds. As it starts to splutter, add this to the rasam.
That's it. Yummy kollu rasam is ready. Serve hot with rice, or enjoy it as a simple soup.
Video
Notes
I prepared this rasam in a very similar way to the goddu rasam without adding any toor dal. But you can also add the cooked toor dal water if you have about 2 tbsps of mashed toor dal.
Adjust salt and rasam powder according to your preference.
Garlic is optional, and if you like the taste of garlic, add more garlic according to your taste preference. You can add up to 5 to 6 big garlic cloves.
I have used tamarind paste here. You can use tamarind pulp, soak gooseberry-sized tamarind in 1 cup for 30 to 45 minutes, and extract the juice.