lightly grease cooker insert; layer and alternate potato slices and onion in prepared cooker. In a blender or food processor, combine celery leaves, parsley, butter, flour, salt, pepper, evaporated milk and cheddar cheese.
Process for 1 minute or until mixture is smooth.
Pour over potatoes and onions, sprinkle with paprika.
Cover and cook on LOW for 6- 8 hours or on HIGH for 3- 4 hours, until potatoes are tender and heated through.