Preheat the oven to 180°C.
Melt dark chocolate and butter together over a double boiler.
In a bowl, mix eggs and sugar.
Add the melted chocolate and butter, and mix well.
Sift in the flour and cocoa powder, then mix to combine.
Pour the batter into a baking pan and smooth the surface.
Bake in the oven for 20-25 minutes.
Let it cool, then cut into desired sizes.