Heat the oil in a large saucepan or wok, add the mustard and cumin seeds and let them pop for 1 minute. Remove the pan from the heat and add the curry leaves, garlic, ginger and chillies. Return to the heat and cook for a few seconds, taking care not to burn the garlic, then add the onion and cook until softened.
Add the turmeric, coriander, cardamom and cloves and cook for a further minute. Add the coconut milk, palm sugar and fenugreek leaves and simmer for 4 minutes. Add the tomatoes and simmer for a further 5 minutes, adding a little water if too thick. Stir in the herbs, season and then serve with rice or lentils and poppadoms.