This is the special cake from Nagasaki. I knew it from my Japanese friend who recommended it before I went to Japan. There are a lot of castella cake brands but she told me to buy it from Fukusaya.
The cake is soft and very sweet, especially at the bottom part where the granulated sugar is concentrated. If you have sweet tooth and looking for something to bring back from Nagasaki, then this is the perfect cake for you. Please mind that the cake can only lasts for a week.
It is available in other city other than Nagasaki as well. For example, Fukuoka. Although I’m not sure about their availability outside Kyushu region.