Prepare the Batter
Wash the rice, urad dal, chana dal, and fenugreek seeds thoroughly. Soak them separately in water for about six hours. Grind the soaked ingredients into a smooth batter, combining them with enough water to achieve a pouring consistency. Add salt, mix well, and allow the batter to ferment overnight or for 8–10 hours until it becomes light and airy.
Prepare the Potato Filling
Heat oil in a pan and add mustard seeds, cumin seeds, and chana dal. Once they begin to crackle, add curry leaves, green chilies, and grated ginger. Sauté briefly before adding the sliced onions. Cook until the onions become soft and translucent. Add turmeric powder and salt, then mix in the mashed potatoes. Stir well until the spices coat the potatoes evenly. Finish with lemon juice and chopped coriander leaves, then keep the filling aside.
Heat the Dosa Pan
Place a flat cast-iron or non-stick dosa tawa over medium heat. Lightly grease the surface with a little oil or ghee and wipe away any excess using a clean cloth or paper towel.
Spread the Batter
Pour a ladleful of batter onto the center of the hot pan. Using the back of the ladle, spread it in a circular motion from the center outward to form a thin, even circle. Drizzle a little oil or ghee around the edges and over the surface.
Cook the Dosa
Allow the dosa to cook undisturbed until the bottom becomes golden brown and crisp while the edges begin to lift naturally from the pan. Cook until the top is fully set and the dosa develops an even crispy texture.
Add the Potato Masala
Place a generous portion of the prepared potato filling in the center of the dosa. Spread it slightly across the middle while keeping enough room to fold the dosa neatly.
Fold and Serve
Carefully fold the dosa over the potato filling into a half-moon or cylindrical roll. Transfer it immediately to a serving plate while it is hot and crispy.
Serving Suggestions
Serve Masala Dosa hot with fresh coconut chutney, tomato chutney, mint chutney, and steaming hot sambar. It also pairs wonderfully with onion chutney, peanut chutney, or a small bowl of vegetable kurma for a complete South Indian meal.