Preheat the oven to 180°C (160°C fan) and line a 9″ square baking tray with parchment paper.
Melt butter and dark chocolate together in a heatproof bowl over boiling water or microwave for 1-2 minutes, then let it cool.
Whisk eggs and golden caster sugar with an electric mixer until pale, mousse-like, and doubled in volume.
Carefully fold the cooled chocolate mixture into the egg mixture without deflating it.
Sift in cocoa powder and flour, then fold gently until combined.
Drain black cherries in kirsch and keep the liquid. Fold cherries, fresh cherries, chocolate chips, and 4 tablespoons of kirsch liquid into the batter.
Bake for 35-40 minutes, then cool completely in the tray.
Drizzle melted dark chocolate over the brownies, sprinkle with chocolate curls, and dust with icing sugar before serving. Enjoy!