400g/14oz Jerusalem artichokes, peeled and cut into small pieces
1 tbsp chopped fresh chives
70驳/2陆辞锄 onions, sliced
250ml/9fl oz chicken stock
salt and freshly ground black pepper
few drops truffle oil
30g/1oz unsalted butter
50驳/1戮辞锄 butter
1 bouquet garni