Preheat your oven to 180°C (350°F).
Melt the dark chocolate and butter together in a heatproof bowl over simmering water.
In another bowl, whisk the sugar and eggs until pale and fluffy.
Gradually add the melted chocolate mixture to the egg mixture, stirring continuously.
Sift in the flour and a pinch of salt, folding gently until combined.
Grease a cake pan and pour the batter in evenly.
Bake for 25-30 minutes or until the top is set.
Let it cool for 10 minutes before transferring to a wire rack.
Once cooled, chill in the refrigerator for at least 2 hours.
Serve chilled with fresh berries on top.