If using fresh corn, boil and remove kernels from the cob. For frozen or canned corn, thaw and drain excess water.
In a bowl, combine corn kernels, rice flour, all-purpose flour, chopped onion, green chilies, grated carrot, coriander leaves, mustard seeds, and salt.
Slowly add water little by little to form a thick, pourable batter—similar to pancake batter consistency.
Heat the appe pan on medium heat and lightly grease each mold with oil.
Pour the batter into each mold, filling about 3/4 full to allow room for rising.
Cover and cook for 3-4 minutes. When the edges start to turn golden, gently flip each appe using a skewer or spoon.
Cook the other side for another 3-4 minutes until golden and crisp. Remove and serve hot with coconut chutney or tomato ketchup.