Wash the idli rice in cold water until the water runs clear. In a separate bowl, wash the urad dal and fenugreek seeds together. Soak both the rice and the dal-fenugreek mixture in ample water in separate bowls for at least four to six hours.

Drain the soaked urad dal and fenugreek seeds. Transfer them to a wet grinder or high-speed blender. Add about 1/4 cup of ice-cold water and grind. Gradually add small splashes of cold water as needed, grinding for fifteen to twenty minutes until the dal becomes a very thick, smooth, fluffy, and voluminous paste that floats when a small spoonful is dropped into water.

Drain the soaked rice and add it to the blender or grinder. Add just enough cold water to allow grinding. Grind until the rice is mostly smooth but retains a very fine, sand-like or semolina-like texture. Do not grind it into a completely smooth paste.

Pour both the ground urad dal paste and the rice batter into a large mixing bowl or container. Ensure the container has plenty of headspace, as the batter will expand. Add one teaspoon of non-iodized salt. Mix thoroughly with your clean hand for two to three minutes to incorporate air.

Cover the container loosely with a lid. Place it in a warm, draft-free place (around 26°C to 30°C / 78°F to 86°F) for eight to twelve hours. The batter is ready when it has doubled in volume, looks bubbly and airy, and has a mild, clean, fermented sour aroma.

Gently stir the fermented batter once or twice from the bottom; do not over-mix or deflate the air. Grease the idli plates with a light coating of sesame oil. Pour a ladleful of batter into each mold, filling them about 3/4 full. Bring two centimeters of water to a boil in your steamer pot, place the idli stand inside, close the lid, and steam on medium-high heat for ten to twelve minutes.

Turn off the heat and let the steamer sit undisturbed for two to three minutes. Remove the idli stand and let the idlis cool slightly. Dip a spoon in cold water and run it gently around the edges of each mold to lift the soft, fluffy idlis out cleanly.