Preheat your oven to 180°C (350°F). Prepare a 20 cm-square cake tin by greasing it and lining it with parchment paper.

In a medium saucepan over low heat, combine the dark chocolate and unsalted butter. Stir until melted and smooth, about 5–7 minutes.

In a large mixing bowl, whisk together brown sugar, eggs, sifted plain flour, and cocoa powder. Gradually incorporate the cooled chocolate-butter mixture.

Pour the brownie batter into the prepared cake tin and bake for 30–35 minutes. Let it cool in the tin on a wire rack.

In a clean saucepan, combine caster sugar and water. Heat over medium flame until the sugar dissolves. Boil until it reaches a golden color, about 8–10 minutes.

Remove from heat and carefully stir in single cream and chopped unsalted butter. Fold in puffed rice cereal until well coated.

Spread the caramel crunch mixture over the cooled brownie base. Allow to set at room temperature for about 30 minutes.

Melt additional dark chocolate and single cream for the ganache over low heat. Pour it over the caramel crunch layer.

Chill the brownies in the refrigerator for at least 3 hours before slicing into squares.