Wgriffin, I think that popping the mustard seeds is the trick. Heat the oil hot but not to start smoking & burn. I do this by closely watching the oil heat up & when I think it’s hot but not too hot, I put just a few mustard seeds in. When they start to pop, I add the rest of the mustard seeds. That way I can monitor the heat & know that the oil is hot enough so they will all pop. One time I cooked the seeds very hot but not too hot & the soup had a wonderful nutty flavor. I would personally try to do this again.
DO NOT add the spices until your seeds are all popping & then you may want to turn your spices heat down a bit, but still simmering your ghee.
In my first two tries, I’ve also burned the mustard seeds. For me, seems that the best is to do them at low heat and keep stirring…it took a bit of a time, but they started popping and they didn’t burn.