Rinse the idli rice and urad dal separately. Soak in separate bowls. Add enough water to cover the ingredients and let them soak for at least 4-6 hours or overnight.

Drain soaked urad dal and transfer it to a blender. The batter should be thick and airy. Then, grind soaked idli rice. The texture should be fine but with a slight grainy texture.

Mix the ground rice batter with the urad dal batter in the mixing bowl. Add salt to taste and mix well using your hands. The consistency of the batter should be thick yet pourable.

Let the batter ferment in a warm place for 8-10 hours or overnight. During fermentation, the batter will rise and become airy.

Grease the idli plates with a little oil. Fill each cavity of the idli plates with the fermented batter. Place the filled idli plates in the idli steamer or pressure cooker.

Steam the idlis over medium heat for 10-12 minutes or until they are cooked. To check for doneness, insert toothpick or knife into the center of an idli; it should come out clean.