I live in a Seafood challenged area and frequently have to buy frozen stuff. The local seafood buyers think that chowder clams, big chewy quahogs are appropriate for for any clam dish. I wanted to make Clams in Black Bean Sauce for a starter tonight and went to my local oriental market and bought frozen Vietnmese Cockle Clams. My other choice was frozen cherrystones and they are just too big. I have steamed the cockle clams and they just refuse to open. Any suggestions? I'm tempted to chuck them out. They don't smell bad but they are sealed up tightly. I've never used them before has anyone?