Roughly chop the tomatoes, stir in the salt and leave to steep for about an hour. Meanwhile, prep all the other ingredients: Peel and chop the garlic and ginger, crush the coriander seeds, finely chop the chiles, peel and finely dice the onions, and peel, core, and chop the apples into 1/3-inch cubes.
Warm the vinegar on a low heat in a small saucepan, add the mustard seeds, then remove from the heat and leave to infuse for 15 minutes.
Put the garlic and ginger into a blender and pulse a few times. Add the vinegar and mustard-seed infusion and blend into a smooth paste.
Heat the oil in a large, heavy-bottomed saucepan on a high heat for 1 minute. Take off the heat for a moment, then add the crushed coriander seeds, cumin seeds, turmeric, nigella seeds, cloves, and paprikas
Fry on a moderate heat for 20 seconds, then add the mustard-vinegar paste and the chiles and onions. Fry for another 5-10 minutes.
Drain the excess liquid from the tomatoes and add to the pan with the apples and sugar.
Reduce the heat and simmer gently for an hour, stirring occasionally.Ladle into warm, dry sterilized jars and seal.
