Soak Cow peas over night in lots of water. Drain the water and Pressure cook it with a some water for 3 whistle. Let it simmer for 5 mins. Switch off the flame and let the pressure go all by itself. Remove and set aside.
Now take cubed yam in a kadai and cover it with water. Add salt to it.cover and cook for 15-20 mins till the yam is completely cooked.
Add the cooked cowpeas in this and mix well.
Now take the grinding ingredients in a mixer and make into a fine paste.
Pour this over the cooked yam and cow peas and mix well.
Let it simmer for 10 mins.
Now make the seasoning. Heat oil and add mustard, urad dal and curry leaves in this. Let it sizzle and crack.