No. 1, which is the way he taught me:

Heat oil in a saucepan, splutter the mustard seeds. Fry the urad dal till lightly browned, add the curry leaves and saute for a couple of seconds.

Now add the onion and the green chillies and cook till the onions become slightly browned. Add the ginger and garlic paste and cook till the raw smell is gone.

Now add the tomatoes, cook on low flame with close lids till the tomatoes get really mashed up. Keep stirring continuously so that it doesn't stick to the pan.

Add water little by little while cooking.

Now add the masalas and cook for another 5 minutes. Add water as required, not too much! Allow to boil till it incorporates all the masala. Adjust the salt and serve warm with rice, dosas, idlis, etc.

No. 2, the way I like to make it:

Chop the tomatoes into big chunks and boil with little water in a saucepan until mushy. Switch off and allow to cool completely. Grind this into a fine paste and set aside.

In a saucepan, heat oil, splutter mustard seeds. Fry the urad dal and the curry leaves for a few moments.

Add the ginger and garlic paste and saute continuously till raw smell is gone. Now add the onion and green chillies and saute till soft. This will keep the crunch of the onion - if you don't like it to bite, then saute more, as simple as that!

Add in the masala powders and saute for around 5 minutes till well done. Add in the ground tomato and bring to boil, mixing in between for the flavors to incorporate.

Add a little water if you find it too thick. Keep on simmer for around 5-7 minutes and switch off. Adjust salt and serve warm.