There are many different types of clam, all under the same name. I tend to stick to the one called Venus clam. Clams are very under-used in Britain, but the French and Americans do use them a lot. I have listed three different recipes here. If you can get fresh cockles, then use them in the recipes instead – to my mind they are superior to clams but difficult to get fresh.
When buying any of the molluscs, always make sure they are still alive; the shells should be tightly closed or they should snap shut as soon as they are handled. They should also be thoroughly washed before cooking. Sit the clams in clean fresh water for about 15 minutes, then change the water, allow them to sit for another 15 minutes, and then repeat the process one more time. If you have been fortunate enough to get hold of fresh cockles, they should be cleaned in the same way.