For dosa dough:
1. Soak urad dal, rice and fenugreek seeds for 7-8 hours.
2. Grind to a fine paste adding water.
3. Put it aside for overnight with lid for fermentation. Next day mix the batter well adding salt. The batter is ready for making dosas.

Potato curry for filling:
4. Mash potatoes roughly into lumps with hand.
5. Heat 2 tbsp of oil in a pan. Add the urad dal,channa dal, mustard seeds, cumin seeds and let them splutter and add curry leaves and fry till light brown.
6. Add chopped green chillis and minced ginger. Mix and immediately add the sliced onions.
7. Fry till transparent,add turmeric and salt. Now add the mashed potato lumps and boiled peas. Mix and sprinkle 3 tbsp of water and let it cook with lid on medium heat for 3 minutes.Turn off heat and adjust salt.

Prepare masala dosa:
8. Heat a griddle. Grease the griddle with oil. Pour one ladle full of batter over the griddle.
9. Spread the batter from the bottom of the ladle evenly making circles. 10. Drizzle oil around the edges of dosa and let it cook on medium heat. The dosa should turn light brown. The dosa generally takes 4-5 minutes to cook on medium heat.
11. Spread potato curry filling in the center of the dosa and fold it towards the center such that it covers the potato curry.
12. Similarly fold the other side also such that it covers the potato curry.

Serve hot with sambar, coconut chutney or peanut chutney.