Butter crocks have been in use in parts of Europe dating back to the Middle Ages, long before reliable refrigeration was available. These airtight ceramic vessels prevent butter from spoiling by blocking out air that can ruin butter. Change the water in the bottom of the crock every few days and store in a cool place to enjoy easily spreadable butter for toast and recipes that require softened butter. Dishwasher safe 2 of them - bought together or separate