Place the dal/dahl (lentils) in two separate bowls and add water. Soak overnight or all day.
When ready to make the batter, drain the water from each of the bowls.
In batches, grind the lentils in a food processor, with a little water, until finely ground, adding water as needed.
Next, grind the rice with a little water, until finely ground, adding water as needed.
Put the ground ingredients into a large mixing bowl. Add salt and more water as needed. You need to have a thin batter to make thin dosas (like crepes).
Heat a nonstick frying pan or griddle over medium-high heat.
Add 1/2 cup dosa batter and quickly spread the batter so that the dosa will be thin.
Next, take a teaspoon of oil and drizzle it around the edge of the frying dosa.
Flip the dosa over when the first side is brown and cook the second side.
Repeat to make more dosas.
Serve with a spicy chutney. You may also stuff the dosa with potato curry or upma. Sambar (a lentil vegetable soup) is great as an additional side.
NOTE: Many people like to add cumin seeds, chilies and onion to the batter, but if you have a spicy chutney or filling, that is not really necessary. The batter will keep better in the fridge if those ingredients are not added.
If new at making dosa, you might want to make your first ones using only 1/4 cup batter until you get the hang of spreading out the batter as it cooks.