1. Whisk yoghurt, salt, red chilli powder, turmeric and half the gram flour together in a bowl.
2. Keep aside. Sieve the other half of the gram flour and soda bi-carb together, add the carom seeds and mix enough water to make a thick batter.
3. Beat well. Add green chillies. Heat enough oil in a kadhai to deep fry.
4. Drop large spoonfuls of the batter in the oil to get 1 1/2 inch puffy dumplings.
5. Fry till golden brown on both sides. Remove and keep aside.
6. Heat 45 ml/3 tablespoons oil in a handi, add the yoghurt mixture and 720 ml/3 cups water.
7. Bring to a boil, reduce to a low heat and simmer for 8-10 minutes, stirring constantly to avoid the yoghurt from curdling.
8. Add the potatoes and onions and cook till potatoes are done.
9. Add the dumplings and simmer for 3 minutes.
10. Heat the remaining 15 ml/1 tablespoon oil in a small frying pan.
11. Add the cumin, mustard and fenugreek seeds and saute till the cumin crackles.
12. Add the whole red chillies. Stir.
13. Pour this tempering over the simmering hot kadhi.
14. Remove to a serving bowl and serve with boiled rice.