Cut the eggplant into slices, about 1 cm thick. Sprinkle some salt and the turmeric and smear them on both sides of the eggplant and keep them aside for half an hour.
After half hour, you will notice that the eggplant has released some moisture. So just drain the water out.
In a frying pan, heat 2 tbsp of mustard oil and when the oil become hot, place the eggplant slices evenly in the frying pan. There should be only one layer of the discs. Cook for 2 minutes on each side or until the eggplants have softened. Remove them from the frying pan and place them on a serving dish.
Dry roast the cumin seeds on a separate pan and grind into a fine powder using a mortar and pestle or a coffee grinder. (see notes)
In a small mixing bowl, mix the yogurt with the cumin powder, sugar and salt to taste. Whisk it thoroughly till you have a smooth yogurt mixture.
In a small tadka pan, take 1 tbsp of mustard oil and heat it. Add the curry leaves, mustard seeds and chilli powder. (See notes)
Swirl the pan till all the seeds start to splutter and then pour half of this oil into the yogurt. Whisk the yogurt once again and pour this flavoured yogurt over the eggplant slices using a spoon.
Make sure that all your eggplan slices are coated with the yogurt. Finally spoon in the rest of the infused oil on the eggplants and allow it to sit for 15 minutes before serving.
This dish tastes great with steamed rice.