Ingredients: 

Red Onions - 2 large
Musturd Seeds - 1tbsp
Urad dal (split black gram) 1/2 cup
Red chillies (as per taste) -  2-3 dried
Whole black pepper 2-3
Pinch of asafoetida / Hing
Tamarind Paste
Curry leaves - few
Salt to taste

Method: 

1 Heat the pan. In 1 tsp of oil, saute mustard seeds, Black gram dal, chilies, black pepper for 1-2 mints.
2 Now add onions, salt and hing.
3. Saute for few mints till the onion become translucent. Switch off the gas and add the curry leaves and tamarind paste and saute.
4. let it cool down and grind to coarse paste

Serve with Idils and Dosa