Tip the cumin, coriander and fennel seeds into a large, dry frying pan set over a medium-high heat and toast until fragrant and lightly browned. Immediately remove from the heat, then roughly grind using a pestle and mortar or spice grinder.

Drizzle the oil into the pan. Add the curry leaves and sizzle for a minute, then add the onions. Fry for around 5 mins until lightly golden. Add the mustard seeds, ground spice mixture, turmeric, salt, garlic and chilli, and fry for another couple of minutes. Tip in all of the tomatoes and fry for a further minute before adding the coconut milk, tamarind and sugar.

Simmer the curry for 25 mins until the tomatoes are really soft and the liquid has thickened a little. Taste for seasoning, and add a little more salt or sugar if needed. Serve hot with the rice.