Zuppa di Mammole e Tompinambur

• 8 large globe artichokes
• 1.5 kg (3.¼ lb) Jerusalem artichokes, peeled

Prepare the globe artichokes by removing the tough outer leaves, then cut off the tops of the leaves. Pare the stalks down to the paler tender part. Slice the artichokes into eighths. Remove the inner choke, which will be prickly and indigestible.

Cut each Jerusalem artichoke into small pieces roughly the same size as the pieces of globe.

Heat the olive oil and the butter in a h