Wash and cut potatos into 2, without removing the skin.
Peel and cut onions into half. (If Madrasi onion is not available the use whatever onions you have and cut then onto four, Adjust the quantity accordingly)
Now in pan, heat 1 tsp oil and put jeera, coriander, ajwain, peppercorn, urad and chana daal. Cook till daal is light brown. Remove from fire and let the mixture cool.
Coarsely grind the above mixture and keep aside.
In a large wok (karahi) heat remaining oil, put garlic, whole red chilly, curry leaves and hing, fry for a minute. Add potatos and onion and cook till potatos are nearly done stirring occasionally.
Now add the daal mixure, salt and garam masala and fry till potatos are light brown and crispy.
Add lemon juice and chopped coriender and mix well.