First boil the potatoes in a pan or steamer or pressure cooker. Then peel and mash them when still warm.
Heat oil in a frying pan. Add the mustard and urad dal.
Allow the mustard seed to splutter and the urad dal to get golden.
Add the chopped onion and saute till they are translucent and soften.
Now add the ginger-garlic paste, curry leaves and green chilies. Saute for a minute.
Add the turmeric powder, asafoetida and stir. Now add the coriander leaves and stir.
Add the potatoes to this mixture or add this sauted mixture to the potatoes. Stir well.
If there is moisture, then you can cook the potato mixture for a few minutes.
Add lemon juice & salt. Mix well.
Check the seasoning and add more salt or red chili powder or lemon juice if required.
Make medium sized balls from this mixture.