Steps
1. Soak rice, urad dal, and fenugreek seeds in water for 6-8 hours.
2. Drain and blend them with a little water to form a smooth batter. Ferment overnight.
3. For the filling, heat oil in a pan, add mustard seeds, and let them splutter.
4. Add onions and green chili; sauté until onions are translucent.
5. Stir in turmeric, mashed potato, coriander, and salt. Cook for a few minutes and set aside.
6. Heat a non-stick pan and pour a ladle of dosa batter, spreading it into a thin circle.
7. Drizzle a little oil around the edges and cook until golden brown.
8. Place a portion of the potato filling on one side of the dosa, fold, and serve hot with chutney.