In a blender, grind the fresh corn, rice flour and gram flour with the yoghurt and a little water to make a smooth, thickish batter similar to idli batter.
Pour the batter into a bowl and stir in the green chilli paste, grated ginger turmeric and chilli powders and asafoetida. Mix well, cover and set aside to ferment for 5-6 hours.
Heat the oven to 180℃. Pour 1 tbsp oil into a 9-inch pie or cake tin, swirl to coat the bottom and place in the oven to heat for 7-10 minutes.
Add salt, 1 tbsp sesame seeds and chopped coriander to the fermented batter and mix well. Add the soda bicarb and gently mix it in. Do not overmix or the batter will deflate.
Carefully remove the heated tin from the oven and pour in the batter. Smooth the top and bake for 45-50 minutes till the sides and top are golden and a skewer inserted into the handvo comes out clean.
Loosen the sides of the pan with a blunt knife, place a plate upside down on the cake tin and unmould the handvo onto it. Heat 1 tbsp oil in a pan and add the mustard seeds. When they crackle, add the remaining sesame seeds and curry leaves and turn off the heat. Pour the tempering all over the top of the handvo. Slice and serve with mint or tomato chutney.