Add buttermilk, turmeric powder, red chili powder, asafoetida, and salt.Mix it well.
keep on stirring and mixing till all the lumps are dissolved and you get a smooth batter. there should be no lumps in the batter. you can also use a hand held beater to mix the batter.
spread oil on plates or boards or tray. large steel lids or thalis work very well. you can also use the back of a large baking tray or your kitchen counter top.Keep your plates ready.
Add 1 cup water in pressure cooker.Put this mixture ready jar in a pressure cooker. turn flame to a medium. Cook the mixture for 3-4 whistles on medium flame.
once the cooker is cool down.Take your jar out and again whisk the steamed batter.
The final consistency of the khandvi batter is shown in below pic. it took 3 whistles for me to get the correct consistency on a medium low flame. the timing will vary depending on the intensity of the flame, the thickness/thinness of the cooker.just do the plate test and when you can form the rolls, then the khandvi batter is ready. if the batter becomes too thick, then it becomes difficult to spread and you don't get thin layers in the rolls.
Quickly pour batter into a large plate and spread thinly & evenly with a spatula. you have to be quick with batter. since even a bit of cooling and the batter becomes likes blob, difficult to spread.
Allow to cool.Cut into equal sized strips.
Gently roll each strip tightly. then place them on a serving tray or plate.if the tray or plate is large, then you will get large rolls. in this case, after you finish rolling half, just cut horizontally and make a second roll.
Arrange the khandvi rolls next to each other in serving plate OR bowl.
Method for tempering:
Heat oil and crackle the mustard seeds.
Then add curry leaves, green chilies and fry for a few seconds.
Add the sesame seeds and when they change color & crackle, pour the hot tempering mixture along with the oil on the khandvi rolls evenly.
Garnish khandvi with some more coconut and coriander leaves, if you prefer.