Gather freshly picked lentil pods1 and stir-fry with pork broth, removing any pork and keeping just the pods.2 If one is stir-frying it plain, then it is better to use more oil. Soft and fleshy ones are the best. Those that are coarse and thin were grown from poor soil and should not be eaten.
扁豆
取現採扁豆，用肉湯炒之，去肉存豆。單炒者油重為佳。以肥軟為貴。毛糙而瘦薄者，瘠土所生，不可食。
Notes:
1Bian dou (扁豆) can either be the slightly poisonous hyacinth bean (Lablab purpureus) or the lentil (Lens culinaris). I am inclined to believe that this is the latter in pod form since lentils pods are prepared stir-fried with pork in Chinese cuisine even today. Furthermore, the former is not commonly consumed.
2Cooking the plant ingredients with meat for its fat and flavour and then discarding it. Wasteful, but not uncommon in the kitchens of the wealthy, then and now.
Sean J.S. Chen 