Rinse the soaked rice and urad dal separately under cold water until the water runs clear. This removes excess starch.

In a blender, combine the soaked rice, urad dal, fenugreek seeds, and 1/2 cup of water. Blend until smooth and slightly thick, adding more water if necessary. The batter should be pourable but not too runny.

Transfer the batter to a large mixing bowl, cover it with a cloth, and let it ferment in a warm place for 8-12 hours or overnight. Fermentation is crucial for the characteristic flavor and texture of dosa.

Once fermented, stir in salt to taste.

In a skillet, heat 1 tablespoon of oil over medium heat. Add mustard seeds and let them splutter.

Add cumin seeds, chopped green chili, grated ginger, and curry leaves. Sauté for 1-2 minutes until fragrant.

Add the boiled and mashed potatoes, turmeric powder, and salt. Mix well and cook for another 2-3 minutes, allowing the flavors to meld.

Remove from heat and stir in chopped coriander. Set aside.

In a blender, combine grated coconut, roasted chana dal, chopped green chili, chopped ginger, lemon juice, and water. Blend until smooth.

In a small pan, heat 1 tablespoon of oil. Add mustard seeds and let them splutter. Add curry leaves and sauté for a few seconds.

Pour the tempering over the blended chutney and mix well. Adjust salt to taste.

Heat a non-stick skillet or dosa pan over medium heat. Lightly grease it with oil.

Pour a ladleful of dosa batter onto the center of the pan and quickly spread it in a circular motion to form a thin crepe.

Drizzle a little oil around the edges and cook for 2-3 minutes until the bottom is golden brown and crispy.

Place a portion of potato filling in the center of the dosa, fold it over, and serve hot with coconut chutney.

Repeat the process with the remaining batter and filling.