Rinse the parboiled rice, regular rice, urad dal, chana dal, and fenugreek seeds thoroughly. Soak them together in separate bowls for at least 6 hours or overnight. Proper soaking ensures the dosa batter ferments well later.

Drain the soaked rice and lentils. Grind them separately into smooth pastes, adding water gradually. Combine the two batters in a large bowl and mix well with your hand for better aeration. Cover and leave to ferment overnight or for 8 to 10 hours in a warm spot until slightly bubbly and airy.

Once fermented, add salt and mix gently. The consistency should be similar to pouring cream, neither too thick nor too runny. Keep aside while preparing the potato masala.

Heat oil in a pan over medium heat. Add mustard seeds, urad dal, and curry leaves. Once they crackle, stir in the green chillies and sliced onions. Cook until the onions turn soft and lightly golden.

Stir in the turmeric powder, then add the boiled, mashed potatoes. Season with salt and mix until the spices are evenly distributed. Add lemon juice and chopped coriander, then set aside to cool slightly.

Place a flat non-stick or cast-iron tawa (griddle) over medium heat. Grease lightly with oil or ghee using a folded paper towel. The surface should be hot but not smoking.

Pour a ladleful of batter onto the centre of the tawa and spread it in a circular motion outward to form a thin crepe. Drizzle a few drops of oil or ghee around the edges for crispness.

Allow the dosa to cook until the edges turn golden brown and the base becomes crisp. Avoid flipping. The top should appear cooked and lightly set.

Spoon a portion of the potato masala into the centre of the dosa. Fold one side over the filling and roll gently into a cylindrical shape. Remove from the pan and place on a warm plate.

Serve hot with coconut chutney, sambar, or tomato chutney. For an authentic touch, brush a little ghee over the top before serving. The crisp texture and spiced filling make every bite deeply satisfying.