Wash the Urad Dal and methi in water for 2-3 times.
Separately wash the rice in water for 2-3.
Soak the Urad dal and methi in one bowl, and Rice in another bowl.
First grind the Urad dal with minimum water to fine and fluffy consistency.
Grind the rice too with minimum water.
Add 1/4 tablespoon of salt and mix everything with hand for at least 2-3 minutes.
Keep it in a warm location for 8-20 hours (depending on location, read above)
Once fermented make Idlis or Dosas as required