After 8 or more hours of fermenting, add in salt, sugar, asafetida, grated ginger and chopped thai green chili along with ⅓ cup of full fat desi sour yogurt and ¼ cup of oil. Mix it well, make sure you have pan cake batter like pouring consistency. Use water if you need to get that consistency.
Start boiling water in the steamer. Spread some oil in the thali you are going to steam the idla in, place it in the steamer while the water is boiling so that the thali starts to warm up.
While water is boiling, take some batter out (just enough for 1 thali of idla) in a small bowl. Add in ¼ tsp of Eno fruit salt and mix vigorously in just one direction. This will form up the batter.
Immediately pour the frothy batter into the thali that is inside the steamer. Spread it evenly in the thali, sprinkle some freshly cracked black pepper and/or red chili powder all over the thali.
Cover the steamer tight so that the steam holds inside. Steam it for upto 10-12 minutes.
Once steamed, take the thali out of the steamer, spread some oil on top and let it cool down for 5-7 minutes.
After few minutes, cut the idla in either square or diamond shapes. Take it out in a big wide bowl. Repeat the steaming process until all the batter is steamed into Idla. I usually end up with 6 thali of Idla, which can vary based on size of your steamer and thali, also depends on how thick or thin you make each thali of idla.
Prepare for tempering as described in next step once all the Idla is steamed, cut and placed in a big wide bowl. You can do tempering/tadka on each thali before cutting it or like me do it all at once after all idla is steamed.