Add asafoetida, red chilies and black gram, and fry, and as it turns to golden colour, remove chillies and black gram, without oil, to a bowl and set aside.
Add the tomatoes to the remaining oil, stir well, cover and cook.
Check and stir periodically, and you can see the skin shriveling and coming off.
Remove from heat, cover and let it cool.
After 10 minutes, deskin the tomatoes, add the fried chillies, salt, tamarind and grind well in a mixer.
Season with mustard and curry leaves.
Goes well with pongal, dosa and steamed rice (with a dash of gingelly oil).