Cut the corn cobs into pieces, mince onion, garlic and ginger very finely together. Fry corn in oil or butter until brown. Remove from the pan and set aside. Now fry the onion, garlic and ginger and when light brown add the turmeric. Cook for one minute and add the rest of the spices and the yoghurt. Cook for about 20 minutes stirring from time to time. Add the corn and salt and cook slowly until the corn is tender. Add the sugar, boil for 1-2 minutes. Serve sprinkled with the green chilli and coriander leaves.