Like mussels, cockles should be live at the point of purchase. They should smell fresh, and the shells should be closed. If any of the cockle shells are open, then give them a good tap against a hard surface. This should encourage it to close - if it remains open, then discard the cockle.
Before cooking, firstly give them a rinse to wash away any sand or dirt. To steam them, pick a large pan with a lid. Bring a cup of water to the boil and add a splash of lemon juice or white wine vinegar. Place the cockles in the pan, and cover. It will only take a couple of minutes for them to cook, and then shells to spring open. The orange cockle inside can then easily be picked out and eaten.
Cockles are often thought of as being a kind of shellfish garnish, served alongside something like a pan-fried fillet of fish. Their use shouldn't be restricted to seafood though. Chef Adam Simmonds, for example, pairs cockles with veal sweetbreads. And chef Phil Fanning, demonstrates how beer-braised cockles can enhance aLancashire Hot Pot. After all, if beef and oysters are a common pairing, then why not lamb and cockles?
Shaun Rankin's recipe for Cockles cooked in white wine with shallots, pancetta and basil demonstrates what a delight simply-cooked cockles can be. Cockles shouldn't be paired with anything too heavy, like a cheese sauce. If, for example, they are being tossed in pasta, then a glug of olive oil, a squeeze of lemon, and a pinch of fresh herbs is often enough to showcase the cockles at their best.