- Roughly peel (not completely) and chop the raw banana. Peel and chop the yam too in similar sized pieces. Wash well and set aside to drain. 
- In a chatti (earthern pot), add the chopped vegetables along with water upto its level, turmeric powder and salt. Bring to boil. 
- Cook till the vegetables are almost done. 
- Meanwhile, grind the coconut with the other ingredients under "for grinding" till it is nice and smooth. Add a little water as needed.  
- Keep the flame on simmer. Whisk the yogurt well along with pepper powder and add into the cooked vegetables. Give a good mix.  
- Add the coconut paste and mix well. Simmer for around 5-8 minutes till the raw smell is gone. Switch off and adjust seasoning.  
- To temper, heat coconut oil, splutter mustard seeds. Fry the dry chillies and curry leaves briefly and add into the gravy.  
- Close and allow the mixture to rest till the time of serving.