Soak tamarind in hot water for 10 minutes. And extract the juice and keep aside.
For grinding
Over medium heat, in a pan, add vegetable oil, chana dal, urad dal, coriander seeds, cumin seeds, fenugreek seeds, and grated coconut.
Dry roast until they become golden brown in color. Allow it to cool.
Add it to the blender jar and grind it to a fine powder. And set aside.
For the seasoning
Over medium heat and in the same pan, add sesame oil, black mustard seeds, and urad dal.
Let the mustard to splutter in the oil
For the curry
Then add chopped onion, saute till it becomes pink.
Now add chopped tomatoes, brinjal and cook for 2 minutes.
Once the purple color of the brinjal changes, add red chili powder and coriander powder. Saute them for 1 minute without burning the spice powders.
Add tamarind extract, ground powder, water, and salt. Bring it to the boil.
Turn to low heat and cook for 15 minutes. This variation of kuzhambu tends to become thicker once it cools down. So adjust water according to your desired consistency.