Melt remaining 2 Tbsp. ghee in same wok, then add a mustard seed. As soon as the oil around the seed starts to sizzle or the seed moves, carefully add remaining mustard seeds, then urad dal (if using) and asafetida. Quickly cover pan and cook, shaking, until mustard seeds start popping more gradually, about 30 seconds. Uncover pan and continue to cook, stirring constantly, until urad dal turns a reddish golden brown and smells nutty, about 45 seconds; watch it closely so dal doesn’t burn. (If you aren’t using the dal, cook mustard seeds and asafetida until seeds are popping, reduce heat to low, and immediately add curry leaves and chile as directed below.)