What is a popular Japanese sponge cake introduced by Portuguese merchants in the 16th century called?

Castella s a kind of "wagashi" (a Japanese traditional confectionery) originally developed in Japan based on the "Nanban confectionery" (confectionery imported from abroad to Japan during the Azuchi–Momoyama period).

The batter is poured into large square or rectangular molds, baked in an oven and cut into long rectangular shapes. Since the recipe calls for "mizuame", a type of sugar syrup, Castella has a moist texture.

Now a specialty of Nagasaki, the cake was brought to Japan by 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 27 cm long.