In a large deep pan or a kadhai combine Bengal gram flour, buttermilk, turmeric powder, red chili powder, garam masala, asafoetida and salt
Mix well using a whisk, till no lumps remain and making sure all the spices are combined well
Heat the mixture on medium flame and keep stirring constantly till the mixture becomes thick
Now take a very small quantity of batter and spread it on a greased thali. Wait for few seconds and try to roll up, if it doesn't roll up smoothly then cook for a few minutes more and check it again till done
While it is still hot, pour portions of the mixture on the thali and quickly spread the mixture in a circular motion into a thin layer with the help of the back of a big spoon
Turn the thali and spread the mixture on the back side of thali
When cool, cut that in about 2-inch strips. Roll the strips and arrange on a plate or a big bowl
For the tempering, heat the oil in a vessel. Add the mustard seeds
When the seeds crackle, add the red chill powder, curry leaves and pour the tempering over the arranged rolls of khandvi
Garnish it with chopped coriander, green chilli and fresh coconut and serve