Heat 1 tbsp oil in a non stick pan (I prefer mustard oil to get the authentic taste). Add cumin and mustard seeds, let it brown and splutter, add the grated onion and ginger and chopped green chili and fry till the raw smell goes off.
Add the mashed potato and all the spices mentioned in stuffing and the salt. Mix on low flame and finally add the lemon juice and chopped coriander. Keep aside and let it cool.
Prepare the batter by adding all the ingredients under batter and mix well so that no lumps remain.
Add 1 tsp of hot oil while making the batter and be sure to make the batter a little thick so that it coats the stuffing nicely.
Heat the oil for deep frying. Divide the potato mixture into equal lemon sized balls and flatten them with your palm.
Dip each flattened piece in the batter and deep fry till golden brown. Make sure you have 1 inch of oil for deep frying in the pan.