While the rice is cooking, prep the eggplant. Trim the stems of the eggplant and cut each one lengthwise into two halves. Then slice each half into 2 or 3 long slices. Line all the slices up and cut them into 1” long pieces. You should now have fat matchsticks of eggplant, each an inch long.
Making the vaggarnae - gather the mustard seeds, urad dal, curry leaves and hing before the next step.
Heat 3 tbsp of vegetable oil in a wide saucepan on medium heat. When the oil starts to shimmer, add the mustard seeds and cover the saucepan while the seeds pop. When the popping is done, lower the fire and add the urad dal.
Wait for the urad dal to turn golden brown (about a minute) and then add the curry leaves.
Finally add the hing and give the vaggarnae a quick stir.
Add the eggplant and stir to combine and coat all the eggplant pieces with the oil. Add 1/2 tsp of salt and stir. Continue to cook the eggplant uncovered on a medium-low fire while stirring occasionally. It is best to avoid stirring the eggplant too much, or they could turn mushy. What you are looking for here is to let the salt draw out the moisture in the eggplant and for the eggplant to cook and caramelize in its own juices.
Be careful not to overcrowd the pan, or let the eggplant burn. If the eggplant looks like it is steaming rather than sauteing, add another tbsp of oil and stir.
When the eggplant is almost done, add half the palyad pudi or Vangi Bhath powder and another 1/2 tsp of salt and stir to combine.
Check the spice and salt in the eggplant mixture and balance by adding more spice powder or salt. You want this mixture to be a little high in salt and spice since you will be adding the rice to it.