Preheat the tandoor or charcoal grill to moderately hot, or alternatively preheat the grill (broiler) to medium-low.
Using a sharp knife, make 4 small holes in each aubergine, then press 2 flakes garlic and 2 cloves into each aubergine and brush with some oil and the turmeric.
Roast the aubergines for 12-15 minutes, turning frequently, until the skin is blackened. Remove and allow to cool, then peel off the skin and put the flesh in a bowl and mash with a spoon.
Heat the ghee in a kadhai, wok, or large, heavy-based frying pan (skillet) over medium heat, add the cumin seeds and stir-fry for 1 minute, or until the seeds start to splutter. Add the onions and stir-fry for about 2 minutes, or until they turn translucent. Add the ginger and chillies and stir-fry for a few seconds.
Add the mashed aubergine flesh, chilli powder, and turmeric and stir-fry for a few minutes, or until the oil separates out.
Now add the tomatoes to the pan and season with salt. Stir-fry for about 5 minutes, or until the oil separates out, then remove from the heat and adjust the seasoning, if necessary. Garnish with chopped coriander.