Peel and cut the tapioca and sweet potato into big cubes. Boil them in a large pot for 20 minutes or until soft. Heat the oil in a pan and fry the anchovies until golden brown. Remove and set aside. In the remaining oil, add the curry leaves, onions, dried chillies and mustard seeds and fry for 2 minutes.
Next, add the boiled tapioca and sweet potato and stir-fry for 2 minutes. Add the salt, turmeric powder and fried anchovies and fry for another 10 minutes. Serve hot.