Melt the dark chocolate and butter together in a double boiler.
Add sugar to the melted chocolate mixture and mix well.
Add eggs and mix until combined.
Sift in the flour and cocoa powder, then gently fold together.
Pour the batter into a baking pan and spread it evenly.
Bake in a preheated oven at 170°C for 20-25 minutes.
Let it cool and cut into your desired size.