Wash 1 cup white whole urad (husked black lentil) 2-3 times with water until the water runs clear. Soak it in 5-6 cups of water for 3-4 hours in a medium-size mixing bowl.
Soak 1 and ½ cup of idli rawa in 3-4 cups of water in another medium-size mixing bowl.
Once the whole urad is soaked, drain the water and add the soaked lentil to the medium jar of a grinder. Add ¼ cup water and grind to make a smooth paste. Keep scraping the sides of the jar while grinding.
Transfer the urad paste to a large mixing bowl.
Drain the water from Idli rawa using a soup strainer and add it to the urad paste.
Add 1 cup ragi flour to the bowl and mix well using a spoon.
Cover the bowl with a lid and keep it in a warm place for 8-10 hours to ferment. You can keep the bowl inside the oven if it is cold outside. The mixture will double in size after it is properly fermented.
Add 2 teaspoon salt and ¼ teaspoon cooking soda to the mixture and mix well.
Keep an idli steamer filled with water over high heat. Grease idli plates with oil and fill the cavities with the batter.
Steam the idli for 10-12 minutes on high heat. Once done, take out the idlies from the plate by sliding a butter knife underneath them. Serve hot with sambar and chutney.
Replace the whole urad with urad dal if you wish to.You can also make this recipe by replacing cooking soda with ENO.ENO has cooking soda as one of it's ingredients and it works perfectly when it comes to recipes like this.