Start grinding the urad dal, toor dal with fenugreek seeds first by adding little water in frequent intervals. When the batter is smooth and fluffy, it's done. Then transfer the urad dal batter to a vessel.
Now in the same blender take soaked rice and add enough water. Grind it to a smooth paste.
Now add the ground rice batter to the vessel in which you have added the urad dal batter. Add required salt. Mix well with your hands. Let it ferment for overnight or at least ten hours.
Next day the batter should be raised as shown. Before making dosas , add required water to bring the dosa batter consistency that is neither thick nor thin. You can make dosas thick or thin as per your preference. Thick dosas are soft and thin dosa are crispy and soft as well. For thick dosas, Heat a pan, spread the dosa thick in circular motion. Sprinkle ½ teaspoon of oil. Cook it for 2 minutes. Once done flip the dosa and cook it for a minute. Remove from the pan once done.
For thin dosas, Heat a pan, spread the dosa thin in circular motion. Sprinkle ½ teaspoon of oil. Cook it for 2 minutes. Once done flip the dosa and cook it for a minute. Remove from the pan once done.