Steam onion and tomato and when cool puree. Mix together yogurt, onion-tomato puree and coconut milk.
Heat ghee in pan, add cumin seeds and when they change colour add curry leaves, green chillies, ginger and sauté for two minutes.
Add asafoetida and sugar, stir and add to the yogurt mixture. Add salt, stir and heat for two to three minutes. Garnish with coriander leaves and serve hot.