Add water chestnut flour, rock salt, red chilli powder and cinnamon powder to yogurt and whisk well. Add four cups of water and mix well.
Heat ghee in a kadai. Add cumin seeds, dry red chillies and curry leaves. Sauté till the cumin seeds change colour.
Add the yogurt mixture and cook till it thickens slightly. Add sugar, salt and mix. Simmer for two minutes.
Garnish with coriander leaves and serve hot.