Chop onion lengthwise, slit green chillies, finely chop coriander leaves and pressure cook potatoes till mushy.

Peel off the cooked potatoes and mash it well. Heat a pan/kadai adding all the "seasoning ingredients" in the order given. When mustard seeds splutter and split black gram lentil turns lightly brown add chopped onions.

Saute for a while till onions turn translucent, now add slit green chillies, turmeric powder, salt and mashed potatoes. Add some water and mix well.

Finally squeeze lemon and add chopped coriander leaves. Masala is ready now.

Heat a dosa griddle/tawa, smear it well with cooking oil. You can use coconut coir for smearing.

Pour a ladle full of dosa batter at the center of tawa and spread it in circular motion with the back of ladle to make thin dosa. Pour a tsp of oil at the edges and center. Cover the dosa with lid and cook for few seconds.

Now when it is cooked well, put a ladle full of potato masala prepared above at the center of masala dosa.

Using flat spatula remove dosa from griddle and fold it half. Serve hot directly from tawa to plate. Coriander-coconut chutney and sambar can be served as side dish.

The crisp crust with soft interior masala dosa is ready.

You can add finely chopped ginger to masala which helps in digesting potatoes.

You can substitute ghee for oil to pour on the dosa.

To learn how to prepare dosa batter, refer my set dosa recipe.