Dosa shell:
1 1/2 cups rice
1/2 cup urad dal
salt to taste
Oil
Masala Filling:
2 large potatoes
1 medium onion (chopped)
1/2 teaspoon yellow split peas
1/2 teaspoon mustard seed
1/2 teaspoon turmeric
1-2 green chili
1 tablespoon oil
salt to taste

Preparation:

Dosa shell

Separately soak rice and urad dal at least 6 hour or overnight in water.
Grind to paste.
Mix together, add salt with water to make batter.
Leave in room temperature overnight.
Mix onion and chilies to the thin batter.
Heat pan or griddle with little ghee or oil.
Spread the mix on pan in circular motion to make thin Dosa.
Cook on both the sides, if desired.

Masala Filling (Spicy Filling):

Heat oil. Add mustard seed, peas, onions and spice.
Fry for about 5 minutes on medium heat or/until onions are turned into golden brown
Add potatoes and mix and cook some more Serve
Add filling inside Dosa and roll. Serve hot with Chutney.