Melt dark chocolate and butter using a double boiler.
Add yuzu marmalade and sugar, and mix well.
Add eggs one at a time, stirring thoroughly.
Sift in cake flour and combine.
Add yuzu juice and salt to finish the batter.
Pour the batter into the pan and spread evenly.
Bake in a preheated oven at 170°C for 20 minutes.
After cooling, garnish with yuzu peel.