Masala Dosa (mashed potatoes filled pancake)

This is a dosa that has a filling of mashed potatoes. The mashed potatoes filling can be prepared in many ways. It can be prepared with onion, without onion, with garlic, without garlic, with tomatoes and without tomatoes.
Generally, a dosa is named depending on the filling used. For instance, a filling of stir fried cauliflower becomes cauliflower dosa. A filling of spicy cottage cheese becomes paneer dosa. A filling of cheddar cheese and green chillies becomes chilli-cheese dosa. Fusion dosa has a filling of fried noodles drizzled in hot and sweet sour sauce. So the choices of filling are endless.
I have presented here the simple masala dosa with onion.

Ingredients:
Dosa batter -2 cup
Boiled and mashed potatoes -2 cup
Onion -2 (finely chopped)
Green chilly- 3 (finely chopped) 
Crushed ginger -1 tsp
Chopped coriander leaves -2 tsp
Curry leaves -few
Mustard seeds -1 tsp
Split black gram -1 tsp
Salt and oil- as required

Method:
Heat some oil in a frying pan. Add the mustard seeds. When it to crackles, add the black gram and fry till it turns brown. Then add the onions, green chilly, ginger and curry leaves. Fry for five minutes. Then add the coriander leaves, mashed potatoes, salt and one cup of water. Cook till everything is blended well. This is the filling.

Next, heat a griddle and pour one ladle of the dosa batter and spread it round to make a thin pancake. Drizzle some oil on top and cook on both the sides.
Then place a spoonful of the filling in the center of the dosa and roll it.

 Serve hot with chutney and sambhar.