serves 6 to 8 Heat the butter in the pressure cooker. Saute the onions until soft, about 3 m inutes. Add the celery and grated potatoes and toss to coat with the butter. Add the grated apples, stock, 1 teaspoon orange zest, and salt. Lock the lid i n place and over high heat bring to high pressure. Adjust the heat to maintain high pressure, and cook for 4 minutes. Let the pressure drop naturally or use a quick-release method. Remove the lid, tilting it away from you to allow any excess steam to escape.
If the soup seems too thin, puree about 1 third of it and stir the puree back i nto the soup. Stir in the remaining half teaspoon orange zest and salt to taste . Heat thoroughly before serving.