Soak the dal together for atleast 1 or 2 hours. The soaked lentils should easily break once you press with your fingernails.
Drain all the water and then add the lentils to the mixer grinder jar. There should be no water at all and none should be added either.
The lentils should be ground coarsely. Steam the lentils by greasing the idli moulds with some sesame oil.
Steam the dal for atleast 10 to 15 minutes. Once cool, pulse the steamed lentils one idli cake at a time. Adding too much would lead to sticky crumble.
You can either stock this in a freezer for a couple of days or make the usili immediately.
Wash and string the french beans, cut them into small pieces.
Pressure cook the french beans with salt for a couple of whistles.
Once the usili or the lentil crumble is ready, heat a kadhai, add 3 tbsp of sesame oil. Add Urad Dal, mustard seeds, few red chillies, curry leaves and some turmeric powder.
Allow the mustard to crackle and then add the cooked beans followed by the lentil crumble. Mix well, check salt and add accordingly.
Switch off the flame and serve with Mor Kuzhambu and Steamed rice.