Preheat the oven to 180°C.
Melt dark chocolate and butter together in a double boiler.
Add sugar and mix well.
Add eggs and blend until evenly mixed.
Sift cake flour and cocoa powder, then add to the mixture and combine.
Pour the batter into a baking pan.
Bake in the preheated oven for 25 minutes.
Let cool and cut into bite-sized pieces.