In a large, heavy Dutch oven, heat oil over medium heat until shimmering. Reduce heat to low and add star anise, cinnamon, cloves, mustard seed, peppercorns and cardamom pods. Cook slowly, stirring occasionally, 30-45 minutes, until the mustard seeds are nearly burnt. Using a slotted spoon, scoop out and discard the spices, leaving the oil in the pan.