Castella (カステラ, Kasutera?) is a popular Japanese sponge cake made of sugar, flour, eggs, and starch syrup, very common at festivals and as a street food.
Now a specialty of Nagasaki, the cake was brought by way of Portuguese merchants in the 16th century. The name is derived from Portuguese Pão de Castela, 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 Madeira cake, also associated with Portugal, but its closest relative is pão-de-ló, also a Portuguese cake.
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 Portuguese: Pão de Espanha, in Greek: Pantespani (Castile is a former kingdom of Spain comprising its central provinces, thus Pain d'Espagne and other variants are quasi-synonymous to "bread from Castile").
A peach castella
Pão-de-ló: kasutera's Portuguese ancestor
Detailed view of a Nagasaki-bought Castella cake
In the 16th century, the Portuguese reached Japan, and soon started trade and missionary work. Nagasaki was then the only Japanese port open for foreign commerce. The Portuguese introduced many then-unusual things, such as guns, tobacco, and pumpkins—and castella. It was able to be preserved for a long period of time, and so 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 an expensive dessert. When the Emperor of Japan's envoy was invited, the Tokugawa Shogunate presented the Castella. Over the years, the taste changed to suit Japanese palates.
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.