Preheat the oven to 180°C (160°C fan forced). Grease a 20cm round spring form cake pan and line the base with baking paper. Make up the brownie mix as directed on the box using the eggs and butter.
Spoon the mixture into the cake pan and gently level the surface. Bake for 25 minutes, or until the surface is dry and the brownie is just firm to the touch. Remove from the oven and leave to cool for 10 minutes.
For the meringue, whisk the egg whites in a large, clean, grease-free bowl until stiffly peaking. Gradually whisk in the sugar, a tablespoon at a time (making sure each addition has been incorporated before adding the next), to form a firm and glossy meringue. Sift over the cocoa powder and gently fold in to give a rippled effect (see Tips).
Spoon the meringue over the warm brownie, leaving a 1cm gap all around the edge. Bake for 25-30, minutes or until the meringue puffs up and is crisp on top. Remove from the oven and leave to cool for 10-15 minutes – the meringue may crack and drop down a little as it cools. Run a palette knife around the edge of the meringue to loosen it from the pan, then gently unclip the pan and leave to cool completely.
Carefully remove the baking paper lining from the base of the brownie cake and transfer the cake to a serving plate. Spoon the whipped cream on top of the meringue and arrange the raspberries, strawberries and cherries on top. Decorate with chocolate curls to serve.