Over medium heat, place a pan, add vegetable oil, black mustard seeds, cumin seeds, and asafoetida.
Wait till mustard seeds get splutter. Then add this to the rasam mixer.
The cooking
Allow them to heat till it becomes frothy(the rasam should neither boiled nor undercooked. So please keep an eye, and wait for the ingredients to start floating on the top).
Switch off the heat immediately, and serve hot with rice.