Large leeks can be tough so select small or medium-sized ones.

Trim the roots and tops and remove any damaged outer leaves. If planning to leave whole, split the green down to the white part and rinse thoroughly under cold, running water. Alternatively, cut into slices, then wash thoroughly to remove any grit.

Blanch in boiling water for 2 minutes. Drain, then 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: 6 months.