Heat the vegetable oil in a large sauté pan or Dutch oven if you do not have one big enough (I used a 14 inch deep sauté pan) over medium high heat. Add the mustard seeds and partially cover the pan. When they have nearly stopped popping, add the cumin seeds. Let them fry for about 60 seconds or so--they will darken and become fragrant. Keep an eye on them as they burn easily.