This recipe is from Christoper Kimball of Cook's Illustrated and America's Test Kitchen. It makes about five dozen rum balls that are intense, fudgy, chewy, complex, and balanced. Recipe can be halved or doubled. Plan ahead, since these are best when left to mellow for at least a few days in the refrigerator. They keep very well and can be stored in the refrigerator for up to a couple of weeks or frozen for up to a few months. Cooking time is refrigeration time. Use vanilla for a non-alcoholic version (sometimes called moon balls).