This classic recipe for clams casino originated in rhode island (in a casino, of course) and is now considered a staple of new england cuisine. Although many variations appear across the country, the essential ingredients in clams casino are bacon and a buttery breadcrumb topping that crisps under the broiler. While these clams may look fancy, they are incredibly easy to make. Not only that, they can be prepared in advance of cooking, and then popped under the broiler just before serving. This recipe specifies littleneck clams, which tend to be quite small, so be sure to choose the largest available. Alternatively, middleneck, topneck, or small cherrystone clams can be substituted. Ideally, the shells will measure 2 1/4 to 2 1/2 inches in size.