In the same pan add remaining oil. Once oil is hot enough, add black mustard seeds and allow it to crackle.
Add onions (sliced or diced) and saute until it turns transparent.
Add Serrano peppers (optional), minced ginger-garlic and curry leaves. Cook for a minute constantly stirring.
Pour tomato pulp (or tomato passata). Cook for 4 to 5 minutes, until tomato is cooked well.
It’s time for spice powders. In goes turmeric powder, chili powder (cayenne pepper), cumin powder, coriander powder and salt to taste. Mix well.
Pour half cup water and let it come to rapid boil.
Add roasted eggplants to the sauce.
Partially cover and simmer cook for about 20-30 minutes. Give a gentle stir once or twice and add water as needed if sauce turns too dry. Do NOT add too much water. Your curry should be thick.
Pour thick full fat coconut milk and stir well.
Wait for a minute and turn off heat.
Garnish with fresh coriander leaves.
Serve hot with rice, roti(flatbread) or biryani.