Blend half of the yogurt, coriander leaves, mint leaves, green chilli, ginger, black salt, one fourth teaspoon cumin seeds till smooth.
Add the remaining yogurt and blend again. Add sufficient water to correct the consistency.
Heat ghee in a non stick pan and add a pinch of cumin seeds and curry leaves. Sauté till curry leaves become crisp. Add this tempering to the yogurt and mix. Serve chilled.