Dice the aubergine, then put them in a colander. Sprinkle with the salt and set aside over a bowl for an hour or so to drain any excess moisture. When ready, pat-dry the pieces with kitchen paper or a clean tea towel.
Meanwhile, dry-fry the cumin, coriander, peppercorns and fenugreek seeds until fragrant, then grind them using a pestle and mortar. In the same pan, dry-fry the mustard seeds and add these to the ground spices together with the paprika and ground allspice. Set aside the mixture.
Finely chop the garlic, chilli & onion, shred the ginger.
Heat the oil in a large, heavy-based pan, then cook the drained aubergine for 10-15 minutes until light golden. Add the spices and stir for 30 seconds, then add the tomato purée.
Stir for a minute, then add the onions, chilli, garlic and ginger and stir to coat well. Add the tomatoes, vinegar and sugar and stir until the sugar has dissolved. Bring to the boil, reduce the heat slightly and cook for about 90-120 minutes, until it has thickened into a jam-like, sticky mixture.
Stir in the lime juice, then spoon the chutney into warm sterilised jars, screw on the lids and rest.
Keep the jars in a larder or cool place for at least 2 weeks before opening. After opening, keep refrigerated - it should be OK for 4-6 weeks.