Heat the oil in a medium saucepan; when it’s hot, add the mustard seeds. As soon as they start to splutter, lower the heat and add the curry leaves. Let them sizzle for 30 seconds, then add the chopped onion.

Fry the onion over a medium heat for 7–10 minutes until golden brown at the edges, then add the tomato and stir-fry for about 30 seconds.

Add the tamarind paste, boiling water, spices and salt and bring to the boil. Simmer over a low heat for 10 minutes until the tomato is cooked through.

Serve hot with freshly cooked rice and poppadoms on the side, or in cups as a drink.

NOTE: This recipe uses the tamarind paste that you can buy at the supermarket, not the very strong tamarind concentrate from an Asian supermarket (if you have this, just use 2 teaspoons). If you’re using a block of tamarind, you’d need a plum-sized portion, soaked in ½ cup of boiling water and then sieved, repeating with a few tablespoons of fresh boiling water until you’ve got all the extract out.