Preheat the oven to 160C(320F) fan-forced and grease and line the base and sides of a 20cm round spring-form tin.

In a large bowl, mix the cocoa and water together until the mixture is smooth.

Add the chocolate, butter, sugar, hazelnut meal and egg yolks to the bowl and stir them through well.

Using an electric mixer or hand-held mixer, beat the egg whites until soft peaks form.

Gently fold ⅓ of the egg whites through the chocolate mixture then fold through the rest of the egg whites just until they are incorporated.

Pour the batter into the tin and bake the cake for about 1 hour.

Let it rest in the tin for about 5 minutes before transferring, right side up to a wire rack to cool completely.

Dust the finished cake with cocoa to serve.