Make the masala by heating the oil and adding the masala ingredients to it, then stir-frying them until the coriander is lightly golden and fragrant. Remove to a blender and, using just enough water, make a smooth paste.
Heat 1 tbsp oil in a deep saucepan. Add the eggplant and curry leaves and cook, stirring, for about 5 minutes until the eggplant is quite tender.
Add the tamarind water, sambar powder, and the ground spice paste and let them boil together for a few minutes.
Add the lentils and simmer 8-10 minutes on a low flame for the flavors to merge
For the tadka, heat the oil in a small saucepan. Add mustard seeds, red chilies and black gram.
Take off heat as soon as the lentils turn golden-brown. Add to the rasavangi.
Garnish with chopped coriander.
Rasavangi tastes absolutely delicious served hot with rice. Enjoy!