Cockles live in heart-shaped, furrowed shells. When uncooked, the flesh inside has an oyster-like sliminess, but it only takes a little blast of boiling water or hot steam for the inside to turn solid and orange - not unlike a mussel.
Cockles are found in estuaries round the British coastline. They lie a couple of inches beneath the sand and are hand-picked at low tide. The size and colour of cockles varies widely, dependent on where they come from. Cockles from The Orkney Islands, for example, are large and cream-coloured, while cockles from the south coast are generally smaller and a darker grey.
For centuries, cockles haven't been considered a particularly prized shellfish. They're thought of as a cockney staple, or perhaps associated with Molly Malone - the fictional fishmonger's daughter in the Irish ditty 'Cockles and Mussels'. More and more though, cockles are creeping into Michelin-style dining, often used as a shellfish garnish to accompany something like monkfish or turbot.
Cockles are low fat, high in protein and sustainable. There is a regulated season though, which starts in late June or July. Cocklers must hold a licence, and they should use sieves to make sure that they don't collect any cockles smaller than the required landing size.
During the summer months, cockles are widely-available at fishmongers, and coastal farmers markets. Toward the end of the season, they are often pickled as a form of preservation, meaning that jars of cockles are available in specialist shops and large supermarkets all year round.