Heat half the ghee in large saucepan over high heat. Add one-quarter of the beef, and cook, turning, for 2-3 mins or until browned all over. Transfer to a plate. Repeat in 3 more batches with remaining beef.
Heat remaining ghee in the pan over medium-high heat. Add onion and cook, stirring, for 5 mins or until it softens. Add the curry paste and garlic. Cook for 1 min or until fragrant.
Return beef to pan and add tomato, 2 cups (500ml) water and vinegar. Bring to the boil. Reduce heat and simmer, covered, for 40 mins.
Meanwhile, combine the cucumber, radish, yoghurt and half the coriander in a small bowl. Place in fridge until required.
Add the sweet potato to the beef mixture and simmer, uncovered, for 40 mins or until sauce thickens and sweet potato is tender. Stir in half the chilli. Divide curry among serving bowls and sprinkle with remaining coriander and chilli. Sprinkle the raita with extra radish. Serve curry with raita and steamed basmati rice.