Wash and soak boiled rice and raw rice for 5 - 6 hours (or overnight ). Grind with grated coconut, tamarind juice, red chilli powder, turmeric powder and salt. (if you add tamarind juice while grinding, then no need to add extra water. If not using tamarind juice, add 3 tbsp water when grinding. Just to cover rice). Grind until the batter is of coarse consistency in a mixer in batches (not very smooth, like sooji / rawa).
Transfer this batter to another container / bowl and mix with asafoetida / hing and finely shredded cabbage.
Add extra water and salt if required and batter should be just like idli batter and of pouring consistency. No need to ferment this batter.
Grease katoris or steel thalis or bowl with little oil and pour this batter up to 3/4th level and steam in a steamer / pedavan / pressure cooker (without weight) for 25 - 30 minutes until done or till a skewer / knife inserted in the centre comes out clean.
Remove from steamer and keep aside to cool for 15 minutes to half an hour.
Gently remove from katoris or cut into desired shape and size from steel thali / steel bowl . The undi slices can be shallow fried in 2 tsp ghee / oil (like pathali bajjille).