Cook tomatoes and onion in 2 cups of water along with chilly powder, turmeric powder, salt and curry leaves.
Grind together grated coconut and cumin seeds to a smooth paste by adding about 1/2 cup of water.
When the tomato and onion is cooked, add the coconut paste and boil for 2 - 3 mins.
:- You can add more water depending on the consistency required.
Add the yoghurt and keep stirring for 1 min so that it doesn`t split.
When done, remove from flame.
Heat oil in a pan or a kadai.
Add mustard seeds, fenugreek seeds, broken red chillies and curry leaves.
After the seeds splutter, pour this into the curry.
:- Serve with hot rice and pappadum.