Castella or Kasutera (Japanese: カステラ) is a sponge cake made of sugar, flour, eggs, and starch syrup. It is popular at festivals and as a street food in Japan. Now a specialty of Nagasaki, the cake is thought to be originally from Spain, brought by way of Portuguese merchants in the 16th century. The name is derived from Portuguese pão de Castella, meaning "bread from Castile". Castella cake is usually sold in long boxes, with the cake inside being approximately 27cm long. It is

somewhat similar to English madeira cake, also associated with Portugal. Note that there are similar types of sponge cakes named after the same fashion, in French: Pain d'Espagne, in Italian: Pan di Spagna, in Greek: Pantespani (Castile is a former kingdom of Spain comprising its central provinces, thus "Pain d'Espagne' is quasi synonymous to "bread from Castile").

During the 16th century, a Portuguese ship came into Nagasaki, which used to be the port of Japanese commerce. The Portuguese brought the Japanese many then-unusual things such as guns, tobacco, and pumpkins. Castella was also one of the things they brought. Castella was able to be preserved for a long period of time, so it was useful for the sailors who were out on the sea for months. In the Edo Period, in part due to the cost of sugar, it was a precious food, and was served to envoys from Korea. Later, Japanese people started making castella, and over the years, the taste changed to fit their palate.

Varieties
Castella is made of natural ingredients, so its simple taste is a favorite of many Japanese people. There are now many varieties made with ingredients such as powdered green tea, brown sugar, and honey. They may be molded in various shapes; a popular Japanese festival food is baby castella, a bite-sized version.