400g/14oz Jerusalem artichokes, peeled and cut into 15mm thick slices
3 leeks, trimmed and cut in half lengthways
10 fresh sage leaves
4 spring onions, trimmed and chopped
50ml/2fl oz good-quality chicken stock
salt and freshly ground black pepper
2 tbsp olive oil
2 tbsp pine nuts
50驳/1戮辞锄 butter
2 tbsp grated Parmesan
3 slices prosciutto, shredded