Melt the dark chocolate and butter together using a double boiler.
Add sugar to the melted chocolate and mix well.
Add eggs one at a time, mixing after each addition.
Sift in the flour and mix to combine.
Pour the batter into a baking pan and spread it evenly.
Bake in a preheated oven at 180°C for 20 minutes.
Let it cool, then cut into bite-sized pieces.