Rinse and soak: Add the idli rice, black urad dal, sago pearls, and fenugreek seeds to a bowl. Wash them together atleast 4 to 5 times until the water runs clear. Now add sufficient water and soak for atleast 6 to 8 hours.
Grind the batter: Drain the water from the rice and dal after the soaking time. Add ¼ cup of water to the blender, add half of the rice, dal, and sago mix, and slightly grind it into a fine batter. It should be slightly coarse. Transfer this ground batter to a vessel. Similarly, grind the next batch. I used the smoothie setting in Blendtec to grind the batter. I used 2 cups of water while grinding and used ice-cold water. Also, rinse the Blendtec with ¼ cup of water and add it to the batter. Add salt and mix well.
Ferment the batter: I used my Instant Pot to ferment the batter. While fermenting the batter in Instant Pot, I do not use the IP lid, and I recommend the same. Use any other lid to cover the IP and set the IP in yogurt mode for 10 to 12. The fermenting time varies between 8 to 14 hours, depending on the weather.
After the batter is fermented, mix the batter gently, add ¼ to ½ cup water and mix well. It should be in pouring consistency.
Heat a well seasoned cast-iron pan, and when it is hot, reduce the heat to medium-low. Take a spoon/ladle full of batter and pour it onto the pan. Slightly spread it, and do not make it too thin or spread as we do for regular dosa. Spread some oil around the edges; ½ tsp should be sufficient.
Cover it with the lid and let the kal dosa cook in the steam. Typically flipping is not required for kal dosa as we let the dosa cook completely in steam. But I flip the dosa and cook for just 10 seconds. That's optional.
When the top part is fully cooked, loosen the edges, cook for 10 seconds, and remove from the pan.
Similarly, make the dosa with the remaining batter and serve hot with chutney, sambar, or vada curry.
Video
Notes
You can use regular idli rice instead of brown idli rice and white urad instead of black urad. Also, you can use an equal measure of raw rice (short grain variety) and idli rice instead of 2 cups of idli rice for this dosa.
Typically, you can make kal dosai without sago or poha/aval. All we need is a good quality of rice and urad dal. Adding these two aids in soft and fluffy dosa. So add either sago or poha, or you can entirely skip it.
I have fermented the batter in Instant Pot. Alternatively, you can keep the batter inside the preheated oven or place it in the oven with the lights on. If the weather is warm and if you live in a warm place, leave the batter outside.