Heat ghee or oil in large pot over low heat; cook onion, garlic, ginger, chilli, spices and curry leaves, stirring until onion is browned lightly and mixture is fragrant. Do not over-brown the onion or else it will give the soup a burnt taste.
Add carrot, apple, potato, lentils and chicken stock to pot; simmer, covered, for about 15 minutes or until vegetables are just tender. Discard cardamom pods and curry leaves.
Blend or process soup mixture in batches until puréed; return to pot. Add tamarind, lemon juice, coconut milk and fresh coriander; stir until heated through.