firstly, in a large mixing bowl soak 2 cup idli rice for 5 hours. alternatively, use dosa rice / sona masuri rice.
in another bowl soak 1 cup urad dal for 3 hours.
drain off the water from urad dal and blend to smooth paste adding water as required.
transfer the smooth and fluffy batter of urad dal into a large bowl.
in the blender take soaked rice and add ¾ cup of washed thin poha.
bend to slightly coarse paste adding water as required.
transfer the rice batter to the bowl of urad dal batter.
mix well making sure everything is combined well.
now cover and rest in warm place for 8-10 hours or till the batter ferments and doubles.
after 8 hours, batter doubles indicating well fermented with air pockets present.
add 1½ tsp salt to the batter and mix well.
mix gently without disturbing the air pockets.
now grease the thatte idli plate with oil.
scoop the batter into idli plate greased with oil.
arrange the idli plate into the stand.
steam for 20 minutes on medium flame or till a tooth pick inserted comes out clean.
finally, thatte idlis are ready to serve along with chutney and sambar.