In a small pan, gently dry roast the coriander seeds until they turn a light brown. Pour straight into a spice grinder or mortar. Add the sesame seeds and coconut to the pan and dry roast these until the coconut is golden. Add to the coriander seeds. Toast the peanuts (if raw) in the same way. Add the peanuts to the seeds and coconut and whizz or pestle to a fine powder.
Heat half the oil in a large saucepan. Add the onion and, once it is soft and colouring on the edges, the ginger. Once the onions are a lovely golden brown, spoon the whole lot into a blender, leaving behind the oil, and add the ground nut powder and 150ml water. Blend until smooth. Pour the remaining oil into the pan and add the remaining whole spices. Once the fenugreek seeds have browned, add the aubergines, give them a good stir in the oil and pour in the onion paste with 350ml water, the salt, turmeric, chilli powder and sugar. Bring to a boil, cover and cook gently for 10–15 minutes, or until the aubergine is soft. The sauce should be like double cream and thickens as it sits so, if necessary, add a splash of water from the kettle.
Add the tamarind and adjust the seasoning and sugar to taste, and serve sprinkled with chopped coriander.