Rinse the urad dal and soak in 2–3 cups water for 5–6 hours with the fenugreek seeds.

Rinse the rice until the water runs clear and soak separately for 5–6 hours.

Drain the dal and grind with 1 1/4 to 1 1/2 cups ice-cold water to a fine paste; transfer to a large container.

Drain the rice and grind with 1 1/2 to 2 cups ice-cold water to a smooth paste, adding only as much water as needed.

Combine ground rice and dal. Add rock salt and mix by hand for 1–2 minutes. The batter should flow freely but not be runny.

Cover and ferment until increased in volume, frothy, and bubbly. In an Instant Pot use the Yogurt setting for about 12–14 hours; otherwise ferment in a warm place.

Use the fermented batter for idli or dosa. For idli, grease idli plates and steam 10–12 minutes on high heat, or about 13 minutes in an Instant Pot with the valve venting.