This is a butter keeper, also known as a French butter crock or butter bell. It is a container used to keep butter fresh and soft at room temperature. It works by creating an airtight seal with water in the base, which keeps the butter fresh and spreadable without refrigeration.  The design consists of two parts: a bell-shaped lid where the butter is packed and a crock that holds a small amount of water.  The butter is stored in the lid, which is then inverted and placed into the water-filled crock.  Butter keepers can keep butter fresh for up to 31 days.  .4.5" tall 3.5" wide