Heat the oil in a heavy bottomed pan then add mustard seeds, urad dal, channa dal and allow it to roast until lighty browned. Once browned, add in the ginger, onions, curry leaves, green chillies and asafoetida.
Saute it for a few minutes until the onions turn soft. At this point add some turmeric powder, salt and potatoes. Stir them well until all the ingredients are well combined.
Cover the pan and turn the heat to low and simmer for a few minutes. Once it is done, turn off the heat. The filling is ready. Keep aside.
Method for making dosa's from the batter
For making dosa's batter, heat the skillet on medium heat. Pour a ladleful of batter over the skillet and spread the batter evenly using a spiral motion from inside out.
Pour a teaspoon of oil or ghee around the edges then Increase the heat and cook for couple of minutes until the bottom of the dosa starts to turn golden brown.
Once it is turning brown, place the filling in the center and fold the dosa from both sides. Remove from the heat and the masala dosa is now ready to be served and eaten.
Serve these delicious ghee roast masala dosa's with chutney.