In a mixer jar, add 1.5 cups of khichdi and 1 cup of water. Grind it into a thick paste and set it aside.
In a pan, add 1 cup of rava and roast it on low flame until it slightly puffs up. Let it cool down and set it aside.
In a mixing bowl, combine the grinded khichdi paste, roasted rava, 1 cup of sour curd, ½ tsp of turmeric powder, and salt. Mix well.
Gradually add 2-3 tbsp of water to make a medium-thick pouring batter. Avoid adding too much water to the idli batter.
Whisk the batter for 2 minutes to incorporate air particles and make it light and fluffy. Cover the batter and let it rest for 20 minutes.
In a tadka pan, heat some oil and add mustard seeds, chana dal, urad dal, chopped curry leaves, and asafoetida. Sauté until the dal turns slightly golden brown. Turn off the heat and add this tadka to the idli batter. Also, add chopped coriander leaves and mix well.
Add Eno fruit salt and lemon juice to the batter. Mix thoroughly.
The instant idli batter is now ready. Grease the idli molds with oil and place a cashew nut in the center of each mold. Fill the molds with batter and place the plate into a preheated steamer.
Cover the steamer with a lid and steam the idlis for 12-15 minutes on high flame. Avoid steaming on low flame.
Once the idlis are cooked, allow them to cool down and then demold them.