Heat the butter in the cooker. Saute the leeks and celery for 2 minutes, stirring occasionally.

Meanwhile, cut the potato slices in half. Add the potatoes and stock. Lock the lid in place and over high heat bring to high pressure. Adjust heat to maintain high pressure and cook for 5 minutes.

Let the pressure drop naturally or use a quick release method. Remove the lid, tilting itaway from you to allow any excess steam to escape.

Puree half of the soup in a blender or food processor.

Pour the puree back into the pot. Stir in the dill (if desired) and add salt and pepper to taste. Reheat thoroughly and serve.

Variation: For a creamier, more elegant version of this rustic country dish, puree the entire mixture, but don't overprocess or the potatoes will becomegummy.