Heat ghee in a kadhai, add mustard seeds, urad daal and chopped cashew nuts. Roast all of these on low flame for few seconds.
Add sooji and roast it for another few seconds and switch of the gas. The idea is not to roast it much, it should not change colour and it should be this hot that you can take sooji in your hands.
You can store this sooji mixture in an air tight container. You can store even a bigger batch of Sooji before hand.
In a big mixing bowl, take roasted sooji add curd, water and salt. Let it rest for 5 minutes.
Mix it well. Now add Eno fruit salt and quickly mix it well.
Grease Idli container with oil and pour this mixture.
Pour little water in the Idli container and steam Idlis for about 12-15 minutes on high flame.
Idlis should cook properly and you can even do the knife/toothpick test.
Serve it with a dollop of ghee on top. Garnish it with coriander leaves.