Firstly wash urad dal several times. Soak them together in enough water for 4 hour.

Wash rice until water runs clear. Soak separately in ample water for 4 hours.

Add rice to the jar and then very little water. Blend to a thick paste.

Add this to the urad dal batter and mix.

Check the consistency. It must not be very thick or very thin otherwise the batter will not ferment well. Check the salt as well and adjust.