Melt dark chocolate and butter together using a double boiler.
Add sugar to the melted chocolate and mix well.
Add eggs and mix thoroughly.
Sift in flour and cocoa powder, and blend evenly.
Pour the batter into a baking pan and smooth out the surface.
Bake in a preheated oven at 180°C (356°F) for 20-25 minutes.
Let it cool completely, then cut into bars.