Methods

1. Drain the yellow lentils and place in a pan with 2 cups of water. Bring to a boil, partially cover and simmer for 20 minutes. 
2. While the lentils are cooking, mash the tamarind by hand or with a fork, and pour into a bowl through a sieve. Squeeze the tamarind to extract as much of the liquid and pulp as possible.
3. When the lentils are fully cooked through, add the tamarind extract to the lentil broth along with the quartered tomatoes, chopped green chilli and turmeric powder. Add ½ cup of water and simmer for 10 minutes. Set aside to cool. (Alternatively place the lentils, tamarind extract, tomatoes, green chilli, and turmeric powder in a pressure cooker along with 1 cup of water. Pressure cook on medium heat to 3 whistles.)
4. Once completely cool, place the lentil mixture in a sieve and press firmly to extract a thick broth. Discard the skins and seeds left behind. 
5. Place the broth back in the pan; add sugar, salt, rasam powder and 1½ cups of water. Mix and boil for 10 minutes. Taste and adjust the seasoning as required. You could thin down the consistency at this point per your preference.
6. Heat the ghee in a heavy bottomed pan over high heat until hot. Add the garlic, and when it turns golden, add the mustard seeds, cumin seeds, asafoetida, dried red chillies and curry leaves. Pour the tempering over the rasam. Garnish with coriander leaves and serve hot with rice, ghee and any crunchy accompaniment. Also, great served as a light soup.

Rasam Powder

1. Separately dry roast each ingredient in a pan, except the turmeric powder, on medium heat until aromatic. Once completely cool, grind all the ingredients to a fine powder in a spice grinder.