Smear oil on the eggplant and roast it on open flame until completely charred and soft inside. You can test this by inserting a knife or a skewer inside.
Once cool enough to handle, peel the skin, mash the eggplant and keep aside. Discard the stalk and skin.
In a kadai, heat the oil. Temper the mustard seeds. Add the chana dal, udad dal and sautxe9 until golden.
Add the red chillies, curry leaves, asafoetida and give it a quick stir.
Add the tamarind paste / puree, rice flour in water and sambar powder in water. Bring this to a simmer.
Add the salt, eggplant puree, turmeric powder and bring to a simmer again.
The consistency will be of a thick gravy, due to the thickening effect of rice flour.
Serve hot with pongal or steamed rice.