Wash the toor dal and pressure cook it for 3 whistles by adding 1 cup of water and 1/4 tsp of turmeric.
Once the pressure is released, allow it cool and mash it well.
If using tamarind, soak a small gooseberry sized tamarind in 1 cup of water for at least 1 hour and extract the juice.
Chop the tomatoes.
Take the vessel, in which you are going to make the rasam. Add the tamarind concentrate/paste, salt, rasam powder, freshly ground pepper, curry leaves, cilantro, tomato, jaggery along with 1.25 cups of water to the vessel.
Mix it well and keep it in the stove and simmer it over a low flame.
When it becomes frothy on top, add the mashed toor dal and the remaining water.
Allow it to simmer till it creates the froth on the top.
In a separate tempering pan, heat the oil or ghee. Add the mustard seeds, hing and cumin seeds. When the mustard seeds start to splutter add it to the rasam.
That's it. Rasam is ready. Serve hot with rice and your favorite dry curry.
Jaggery is optional.
Adjust the salt and rasam podi as per your preference.
If you prefer very thin consistency rasam, add one more cup of water and adjust the salt accordingly.