Heat ghee or oil in a frying pan over medium heat. Add the mustard seeds and let them splutter. Add the chana dal, urad dal, and cashew halves. Fry for 1 to 2 minutes on low-medium heat until the dals turn light golden and the cashews are pale yellow.

Add the finely grated ginger, chopped green chilies, chopped curry leaves, and a pinch of asafoetida (hing). Sauté for about 30 seconds until the raw aroma of ginger disappears.

Turn the heat to low and add the rava (semolina) to the pan. Roast, stirring constantly, for 3 to 4 minutes. The rava should become fragrant and warm to the touch, but do not let it change color or turn brown. Turn off the heat and transfer the roasted mixture to a large mixing bowl to cool slightly.

To the cooled rava mixture, add the yogurt, 1/2 cup of water, salt, and chopped coriander leaves. Whisk gently to combine into a thick batter without lumps. Cover the bowl and let the batter rest for 15 minutes. The semolina will absorb the liquid and thicken significantly.

While the batter rests, add 2 to 3 cups of water to your idli steamer or deep pot and bring it to a boil. Grease the idli plates thoroughly with a thin layer of oil or ghee. If desired, place one cashew piece at the bottom of each mold.

Check the rested batter. If it has become too dry and thick, add 1 to 2 tablespoons of water to bring it back to a thick dropping consistency (like a thick cake batter). Sprinkle the Eno fruit salt evenly over the batter. Pour 1 teaspoon of water directly onto the Eno to activate it; it will begin to bubble and foam immediately.

Gently fold the foaming Eno into the batter using a spatula. Do not over-mix; stop as soon as the batter looks light, aerated, and uniform. Working quickly, spoon the batter into the greased idli molds, filling each to about 3/4 full to allow room for the rise.

Place the idli stand inside the steamer once the water is boiling vigorously and releasing steady steam. Cover with a tight-fitting lid and steam on medium-high heat for 10 to 12 minutes. To test for doneness, insert a toothpick into the center of an idli; it should come out clean without any wet batter sticking to it.

Turn off the heat. Remove the idli stand from the steamer and let it cool for 3 to 5 minutes. Dip a spoon in cold water and gently slide it around the edges of each idli to scoop them out of the molds cleanly.