Soak medium gooseberry sized tamarind in hot water. After sometime squeeze the tamarind to get the tamarind juice> keep it aside.
In a kadai fry the red chillies, coriander seeds, thuvar dal and chana dal
Add fenugreek seeds at the end so that it doesn't become bitter
Fry the spices till the dal becomes golden brown and spread it in a separate plate for faster cooling
Ground the spices into a coarse powder
Take oil in a kadai
Add mustard and curry leaves
When mustard splutters, add the onions and fry till onion turns slightly brown.
Add turmeric powder and fry till its aroma goes
Now add the tamarind juice and 1 cup water
Add salt as per taste
As the tamarind water is boiling add the drum stick pieces. Let it cook for few minutes.
Once the drum stick is cooked add the ground spice powder
Boil the kuzhambu till the gravy thickens.
Now transfer the kuzhambu to a serving bowl and serve it along with rice