Cook and mash about 15 medium size potatoes (6.5 cup).
Crush ginger and garlic.
Grind chili's and crush coriander seeds.
In a pot heat 6 tbsp oil. Add mustard seeds. When mustard seeds starts to sputter, add turmeric powder, asafoetida, crushed ginger, garlic, green chilies, coriander seeds and fry on low heat for 2 minutes.
Chop coriander leaves and curry leaves an add it to the tadka. Let it cool.
Add the above mixture and salt to the mashed potatoes. Mix well.
Make around 50 batata wada (around 2 inch diameter) patties.
Make a batter by mixing gram flour (besan), rice flour, turmeric powder, chili powder, ajwain seeds, salt and water.
Dip the batata wada patties into batter.
Fry them in oil on medium heat till golden brown.
Serve them stuffed in bun which has been spread with chutney.
Notes
You will get medium spicy wadas from this measurements. You can add more green chilis if you want more spicy wadas.