In Gangseo District in Seoul, you’ll find a cake shop called Laoje Castella and an incredible chocolate castella. One slice costs KRW 12,000 which is about £6.83/$8.64 but that slice might take two separate sittings depending on your appetite.
The above video shows the baking process, starting with a lot of eggs (must be well over 100) with the yolks separated from the albumen and the ingredient adding and mixing begins.
Castella related: how to make a Taiwanese Castella and another giant castella.