Boil the potatoes gently in salted water until tender, then drain well. Leave them to cool slightly.
Fry the pancetta or bacon until crisp, break up, then set aside. Fry the breadcrumbs in the pancetta or bacon fat until crisp.
Slice the potatoes in half and dress with the soured cream, yoghurt, sea salt and freshly ground black pepper. Fold in the pancetta and most of the breadcrumbs and scatter the top with the chives and remaining breadcrumbs before serving.