A passive cooling container assembly for keeping food cool is disclosed. The assembly comprises an outer, thermally-insulating shell and an inner, thermally-conductive shell nested into and possibly affixed to the outer shell. The inner shell has a recessed volume at a bottom of the inner shell. A removable cold disk is provided and is configured to rest within the recessed volume of the inner shell. The cold disk comprises a material which may be thermally cooled and permanently encapsulated within a casing. The cooling container assembly also includes a removable food container capable of being nested into the inner shell. Optionally, a removable lid is also provided which fits onto the food container.