Begin with making the corn puree. Use a sharp knife to cut down the length of each cob, close to the core, to remove the kernels (you will need about 1½ cups kernels).
Heat the oil in a saucepan over medium heat. Add the onion and garlic. Cook for 3-4 minutes or until onion is softened. Add the corn and cook, stirring, for 2-3 minutes. Add 160ml (⅔ cup) water a