In a small pan, heat the oil or ghee. You want it to come up to 340 F or 170 C.To test this, add one single mustard seed, if it pops and cracnkles, the oil is ready.
Add the cumin first. It should split and splutter and turn brown. If it turns black, the oil is too hot.
Reduce the heat to medium now.
Add asafetida (hing) , chopped onion and garlic. If using, add green chili and coriander seeds next. Use a spoon to move things around.
The garlic should start to turn golden brown on the sides.
Switch off the heat, add the dry ground spices- turmeric, coriander powder and red chilli powder.
Whisk the yogurt in a bowl.Add the tempering to it.
If needed, add a little water to adjust the consistency.