Method:
Curds are required at the rate of cup per 4 to 5 vadais.

To the curds add minced ginger, chopped green chillies and salt, according to taste.
Soak black gram bondas or masal vadais in it, when cool.
Season with mustard and curry leaves in oil.
Keep aside and serve after an hour.

If thayir vadais are required immediately, dip the hot masal vadais/ black gram bondas in cold water first, take them out in 2 minutes and then drop into curds, previously seasoned as above. (Don't drop bondas/vadais in curds, when they are hot.)