Heat a pan on low flame. Add vegetable oil. When oil gets hot, add mustard seeds. When they splutter, add bay leaves. After 1 min add onions and fry well. After onions turn golden, add chopped tomatoes. When they are half cooked, drain all the water and add the slit brinjal. Increase the flame and fry the brinjals. Add more vegetable oil if needed.
Meanwhile, take tamarind and soak it in a big glass of warm water for 1/2 hour. Use your hands to mash and extract tamarind juice and pulp.
Add salt, chilli, coriander powder, turmeric to the tamarind pulp/juice. Mix well and add to the fried brinjal.
Keep the flame on high and cook brinjal till it boils. Check for salt. Serve!