Heat the 2 tablespoons oil over medium-high heat in a large frypan and fry aubergine pieces until golden, about 5 minutes. Remove the aubergine from the frypan and set aside; wipe out the frypan with a paper towel.
Heat the 6 tablespoons oil in the same frypan over medium heat. Stir in the cumin, fenugreek, kalonji and sesame seeds and cook until the cumin turns golden, about 2 minutes. Reduce the heat; stir in the ginger and garlic and cook for a few seconds. Stir in the onions and green chilli and continue to cook and stir until the onion is golden, about 10 minutes.
Stir the tomato puree, chilli powder, coriander, turmeric and salt into the onions. Cook and stir over medium heat for 2 minutes or until the oil separates. Stir in the cooked aubergine; cover and simmer until aubergine is tender, about 5 minutes. Pour in the coconut milk; stir until blended and heated through. Sprinkle with coriander leaves.