Heat oil in an iron tawa (griddle).
Fry the urad dal papads in the oil until crisp. Remove and set aside, draining excess oil.
In the same hot oil, add cumin seeds and curry leaves.
Add chopped onions and saute until well browned.
Add coarsely crushed green chillies and garlic. Saute for 2 minutes until the raw smell disappears.
Add a little hing powder and chopped tomatoes. Saute for 2-3 minutes.
Add a little turmeric powder and mix well.
Reduce the flame to low. Add Kolhapuri masala (or onion-garlic masala) and garam masala powder. Saute well.
Add the boiled, cooled, and mashed potato. Mix and saute, mashing it further if needed.
Add the farsan and mix well to combine with the masala.
Crush the fried papads and add them to the mixture. You can skip papad if you've added farsan, but it adds a nice taste.
Add roasted and coarsely crushed peanuts. Saute on medium heat for 1-2 minutes.
Add salt carefully, considering the saltiness of farsan and papad. Mix well.
Add chopped coriander leaves. Mix Well.
Sprinkle a very small amount of water. If you added salt while sauteing onions, you might not need water unless you want a more gravy-like consistency.
Mix well and reduce the gas to very low.
Cover with a tight lid and cook for 2 minutes.
If you prefer a drier bhaji, don't add water. For a slightly wetter consistency, add a bit more water.
Turn off the gas.
Squeeze lemon juice over the bhaji just before serving.
This bhaji is very tasty and can be eaten with jowar bhakri, chapati, or bajra bhakri. It's also a good option when you don't have other vegetables, especially during rainy days.
Your "Farsan Bhaji" is ready to be served.