It is said that the current method of using two pieces of castella to sandwich the bean paste was the idea of the Japanese cake shop in Ueno called 'Usagi-ya' which was founded in 1914, and this method became popular around Japan.
現在の二枚のカステラ風の生地で挟む方式は大正3年（1914年）創業の上野の和菓子屋「うさぎや」にて考案され、全国に広まったとされる。