Place the brinjals in a plastic bowl and sprinkle with the salt. Leave them for 2 hours and then gently press out and drain off the liquid.
While the brinjals are marinating, place the garlic, chillies and ginger in a food processor, together with 1 pint of vinegar, and process to a smooth purée.
Grind the fenugreek, cumin and mustard seeds to a powde