Wash and rinse the rice and daal. Place the rinsed rice, daal and fenugreek seeds in a large bowl and cover several inches with non-chlorinated water. Cover and soak overnight.
Drain but do not discard the soaking water. Place the drained rice, daal and fenugreek in a high speed blender. Add 1 cup of the reserved soaking water. Blend until smooth with a little graininess remaining. Pour the mixture into a large non-reactive bowl (eg, glass, stainless steel), very loosely cover with plastic wrap and place the bowl in a warm place for 24 hours, until the batter is puffier and a little bubbly when stirred. (Optional: You can stir in a teaspoon of sugar to help aid in fermenting.)
Stir in the salt along with enough water to create the consistency of thin pancake batter. You can test the readiness of the batter as follows: Fill a glass with water and drop a little batter into - if it floats it's ready. Heat a large nonstick pan over medium-high heat. (Traditionally a tawa or tava is used. I'm using my professional crepe maker. There are also many less expensive crepe makers available that will do the job. I used this one for a couple of years before upgrading to my current one.) Flick some water onto the hot surface and if the beads of water sizzle and evaporate the cooking surface is ready. Melt a little ghee on the cooking surface or spray with a little cooking oil. Pour a ladle-full of batter onto the cooking surface and immediately use the round bottom of the ladle to move in a spiral patter from the center of the batter outward to form a crepe. Wait a few seconds and then very lightly drizzle a little olive oil over the crepe. Once the bottom is lightly browned flip the dosa over and continue to cook until lightly browned. Transfer to a plate in a warm oven and repeat with the remaining dosa batter. Makes 12 9-inch dosas.