Wash the eggplant well, pat dry with a clean kitchen napkin. Cut into big chunks, place in salted water for 5 mins. Remove from the water and leave them on a clean cloth to dry out under direct sunlight for a few hours. You can do this for 2 days if required.

Dry roast the mustard seeds until they begin to pop, transfer to a clean sheet of paper, crush them with a rolling pin to break apart the husk. Discard the husks as much of it as possible by gentling blowing it off.

Make a fine paste of the red chillies, 10 garlic cloves and 1-inch ginger piece, using about 1 cup vinegar, adding in increments. Slice the remaining garlic into thin pieces and the remaining 1 inch ginger into juliennes

Heat oil in a heavy bottomed kadai/pot, add garlic, saute until fragrant. Then add ginger saute for another few seconds. Add curry leaves, saute until they turn crisp.

Add the ground paste, stir-fry the paste on medium heat, until the rawness is gone away, about 3-4 minutes.

Extract the remaining paste from the blender using the remaining 1/2 cup vinegar, and add to the pot along with sugar, salt, and the mustard powder.

Add the dried eggplant pieces, and mix well with the masala. Simmer another minute and switch off the heat. Once it cools down, store in a sterilized airtight container. Let it mature on the countertop for about 2 weeks. You can store it at room temperature or in the refrigerator.