Melt dark chocolate and butter together using a double boiler.
Beat the eggs and mix them with the sugar.
Gradually add the egg mixture to the melted chocolate mixture, stirring well.
Sift in the flour and gently combine until smooth.
Pour the batter into a mold and level the surface.
Bake in a preheated oven at 170°C (338°F) for 20 minutes.
Let it cool, then cut into bite-sized pieces.