Heat the butter in the cooker. Saute the anise seeds for 10 seconds, stirring constantly. add the leeks and saute for 2 minutes, stirring frequently. Stir in the celery, stock, and orzo. Lock the lid in place and over high heat bring to high pressure. Adjust heat to maintain high pressure and cook for 3 minute s. Reduce pressure with a quick release method. Remove the lid, tilting it aw ay from you to allow any excess steam to escape. If the orzo or celery is not quite done, cook over medium heat, uncovered, for another minute or two. With a slotted spoon, remove about a third of the celery and orzo. Puree in a food processor or blender, then stir back into the soup. Reheat if necessary. Add salt to taste and serve immediately.