Prepare Batter:

1. Soak Ingredients:
   • Wash the rice and dals several times until the water runs clear. Soak the rice, urad dal, and chana dal together in clean water for a minimum of 6 hours. Soak fenugreek seeds separately.
2. Grind Fenugreek Seeds:
   • Grind the soaked fenugreek seeds to a fine paste using a little water.
3. Grind Rice and Dal Mixture:
   • Grind the soaked rice and dal mixture to a slightly grainy consistency (not as coarse as rava but not too smooth). The batter should be pourable but not too runny.
4. Combine and Ferment:
   • Mix the fenugreek paste and rice/dal batter together by hand, which helps with fermentation. Add a tablespoon of sugar to aid fermentation and enhance the taste.
   • Ensure enough water is in the batter; it should be slightly runny for proper fermentation.
5. Ferment the Batter:
   • Use an Instant Pot’s yogurt setting for 8 hours with an external plate (not the one that comes with the Instant Pot). Alternatively, preheat your oven to 120°F for 8 minutes, turn it off, keep the light on, and place the batter inside the oven to ferment. Fermentation may take longer with this method. The batter should have bubbles and a slight rise, but do not over-ferment.
6. Store and Use:
   • Once fermented, gently mix the batter. Use what you need for the day and store the rest in the refrigerator for up to two weeks without adding salt.

Prepare Potato Filling:

1. Cook Spices:
   • In a pan, heat oil. Add mustard seeds and let them splutter. Add cumin seeds and curry leaves.
2. Sauté Ginger and Chilies:
   • Add grated ginger and chopped green chilies. Sauté until fragrant.
3. Add Potatoes and Spices:
   • Add the mashed potatoes, turmeric powder, and salt. Mix well and cook for a few minutes until everything is heated through.
4. Garnish:
   • Stir in chopped coriander leaves and lemon juice. Mix well and set aside.

Cook Masala Dosas:

1. Prepare the Tawa:
   • Heat a tawa (griddle) on high heat. Once hot, reduce to medium-low. Rub the surface with a little oil; if there’s excess oil, wipe it off. Too much oil will make it harder to spread the dosa batter.
2. Cook Dosas:
   • Pour a ladleful of batter onto the tawa and spread it in a circular motion to form a thin dosa. Add a little ghee or oil around the edges to help the dosa lift easily.
   • Cook until the dosa is golden and crisp on the bottom. You can flip it to cook the other side if desired, though traditional dosas are often cooked only on one side.
3. Add Filling:
   • Place a portion of the potato filling in the center of the dosa. Fold the dosa over the filling and serve immediately.
4. Serve:
   • Serve hot with coconut chutney, sambar, or any other preferred side.