Steps
1. Rinse the rice and urad dal together and soak them with fenugreek seeds in water for 6 hours or overnight.
2. Drain and blend the soaked mixture with a little water to form a smooth batter. Let it ferment for 8-12 hours until it rises.
3. In a pan, heat 1 tbsp of oil, add mustard seeds, and let them splutter. Add chopped onion, green chili, turmeric powder, and mashed potatoes. Mix well and cook for 2 minutes. Set aside.
4. Heat a non-stick skillet and pour a ladleful of dosa batter, spreading it into a thin circle. Drizzle a little oil around the edges and cook until it turns golden brown.
5. Place a portion of the potato filling in the center and fold the dosa. Serve hot with coconut chutney and sambar.