Kasutera (カステラ) is a sponge cake made of sugar, flour, eggs, and starch syrup. It is a speciality of Nagasaki, but the cake is originally from Spain, the name believed to derive from region called Castilla. During the 16th century, a Portuguese ship came into Nagasaki, which used to be the port of Japanese commerce. The Portuguese brought Japanese a lot of unusual things such as guns, tobacco, and pumpkins. Kasutera was also one of the things they brought. Kasutera was able to be preserved for a long time of period, so it was necessary for the sailors who were out on the sea for months. In the Edo era, it was a sweet that was precious and was served for the envoys from Korea. Later, Japanese people started making kasutera, and it slowly changed the cake's taste that fit to their palate. This is the root of the kasutera in today's Japan.

Kasutera is made of natural ingredients, so its simple taste is a favorite of may Japanese people. There are now many kinds of kasutera, made with various ingredients. For example, there are kasuteras made with powdered green tea, and brown sugar.