1 Preheat the oven to 120°C (250°F). Line two baking trays with parchment paper and trace a 20 cm circle on the underside of each sheet as a guide.

2 In a perfectly clean, grease-free bowl, whisk the egg whites to soft peaks. Gradually add the caster sugar a spoonful at a time, continuing to whisk until the meringue is glossy and holds stiff peaks.

3 Gently fold in the sifted cocoa powder, cornflour and salt, then fold in the vanilla extract until the mixture is even in colour and texture.

4 Divide the meringue between the two traced circles. Use a spatula to spread each into an even disc about 1.5–2 cm thick.

5 Bake the meringue discs for 60–70 minutes until they are dry and crisp on the outside. Turn off the oven and leave the meringues inside to cool completely for at least 1 hour (this helps prevent cracks).

6 While the meringues cool, prepare the chocolate ganache: chop the dark chocolate and place in a heatproof bowl. Heat the cream until just simmering, pour over the chocolate and let sit 1–2 minutes. Stir until smooth, then add the butter and icing sugar and mix until glossy. Cool until spreadable.

7 To assemble, place one meringue disc on a serving plate. Spread half of the ganache evenly over it. Carefully place the second meringue on top and spread the remaining ganache over the top and sides.

8 Chill the assembled cake for 20–30 minutes to set the ganache slightly, or serve immediately at room temperature for a softer finish.

9 Dust the top with extra cocoa powder and decorate with fresh berries before serving. For clean slices, run a knife under hot water, dry it, and slice between servings.