For the dosa: Soak the parboiled and uncooked rice together in water.
Separately, soak the dal and fenugreek seeds together in water.
After 3-4 hours, drain and reserve the water and grind both separately in a blender to a fine paste, adding some the reserved water as needed (if the grinder/blender seizes up) until the mixture is of batter consistency.
Add the salt, some water if necessary, and mix both together thoroughly; keep overnight to ferment.
The next day, check the batter; if too thick, add some water and mix so that it is of a pouring consistency.
Heat a skillet and grease with some oil.
Pour a ladleful of batter and spread as quickly as possible into a thin circle.
Pour a little oil (about 1/2 teaspoon) all around the crepe and on the centre as well.
Cook until the dosa is done, then turn over and cook the other side until crisp.
Set the dosas aside.
Note: If parboiled rice is not available, soak 2 1/4 cups of uncooked rice.
For the potato curry: Heat the 3 tablespoons of oil.
Season with the mustard and gram dals.
When done, add the chopped onions, green chilies, ginger, curry leaves, chili powder, and turmeric powder.
When the onions are browned, add the potatoes and salt, and mix thoroughly.
Add the coriander leaves and lemon juice, if desired, and mix well.
For the chutney: Heat the oil, add the asafoetida, red chilies, and then the dal.
Fry until the dal turns brownish.
Remove from flame.
Grind this mixture with the grated coconut, salt and tamarind to a slightly rough paste.
Add a little water to make the chutney of a spreadable consistency.
To make the masala dosas (the final product!): When required, reverse the prepared dosa and place on a skillet.
Spread approximately 1 tablespoon of chutney evenly all over the dosa.
Carefully place 2 tablespoons of potato curry in the centre, fold the the left a third over the centre, and then the right side over the left (or, just fold it any way you like!).
Sprinkle a little ghee or butter.
Roast for a minute or two.
Remove from flame and serve immediately.
Alternatively, stuff the dosa with the potato curry only, and serve the chutney as a dip.