Boil the potatoes, peel and mash them.
in a kadhai, heat oil, add mustard seed, ginger garlic, hing, curry leaves, green chillies, coriander, turmeric, salt and mashed potatoes.
mix well and let it cool.
Once cooled, make small lemon size balls and flatten them on your palm.

For the cover, take chickpea flour in a bowl, add salt and turmeric and water little by little to form a semi thick batter. add soda and mix well.
Heat oil in a kadhai.
Dip the vadas in the batter and fry them from all the sides.
Fry some green chilles to eat with the vadas.