Avoid the largest specimens, as they will be woody. Choose medium-sized ones with firm stalks.

Cut off any stalks and leaves. Peel and cut into even-sized chunks.

Blanch in boiling water for 2 minutes. Drain and plunge immediately in a bowl of iced water to cool. Drain again and dry on kitchen paper. Pack in convenient quantities in polythene bags. Remove the air, seal, label and freeze. Storage time: 12 months.