Pressure cook 2 tbsp of toor dal with 1 cup of water, ½ tsp turmeric powder, and a few drops of oil for 3-4 whistles. If using an Instant Pot, cook the dal using the pot-in-pot method for 20 minutes.
Once cooked, let the pressure release naturally, mash the dal, or you can even grind it smoothly like how I did and set it aside.
In a heavy-bottomed pot (such as an eeya sombu tin alloy vessel), combine tamarind paste, 2 cups of water, salt, rasam powder, curry leaves, ¼ tsp dried neem flowers, and red chilies (broken into small pieces).
Heat the mixture over medium flame and allow it to simmer. Once the mixture starts to boil, add the mashed dal along with another cup of water.
Let it simmer until frothy. Turn off the heat once the froth forms.
In a small pan, heat the ghee. Add toor dal, cumin seeds, mustard seeds, and the remaining dried neem flowers. Sauté until the neem flowers turn slightly brown.
Pour the tempered mixture into the rasam and mix well. Serve warm as a soup or with rice, paired with poriyal or kootu.
Notes
Adjust the rasam powder based on your spice preference. This rasam is relatively mild.
You can add up to 3 tsp of dried neem flowers for a more intense flavor.
The total water requirement for this rasam is 4 cups.
If you don't have tamarind paste, soak a gooseberry-sized piece of tamarind in 1 cup of water, extract the juice, and use it in the rasam.
I did not add any cilantro as wanted the flavors of neem flowers to shine.