A small square container with a square seal that I hear people use to store butter.
Note these are unused Tupperware items in fantastic condition. They are vintage and as they are vintage they do not carry a warranty.
Listing is for 1, two are available
Allegra Reverso Serve And Gather - INSERT ONLY
Eco Bottle Square 1L
Fridge Cool Mates - Various
Midgets - Set of 4