Preheat the oven to 180°C.
Melt the dark chocolate and butter together over a double boiler.
Add the sugar and mix well.
Add the eggs and whisk.
Sift in the cake flour and cocoa powder.
Mix all the ingredients evenly.
Pour the batter into a baking pan.
Bake in the oven for 25-30 minutes.
After cooling, cut into desired sizes.