Remove duck from pan and transfer to a warm place, cover loosely with foil and set aside to rest. Return pan to medium-high heat and add reserved rendered duck fat. Add mandarin halves cut-side down and cook until golden (1-2 minutes). Add honey, vinegar, mandarin juice, star anise, cinnamon and bay leaves, and cook until reduced and sticky (3-4 minutes). Return duck and any resting juices to the plan, season and serve.