1.Preheat oven to 180°C. Grease a deep 22cm round springform pan; line base and side with baking paper.
2.Place cacao, butter and chocolate in a large heatproof bowl over a medium saucepan of simmering water (do not allow base of bowl to touch water). Stir until melted and smooth. Remove bowl from heat; cool for 15 minutes.
3.Meanwhile, combine coffee and the boiling water in a heatproof jug. Beat eggs and sugar in a small bowl with an electric mixer for 2 minutes or until thick and creamy. Stir in coffee. Add egg mixture to chocolate mixture; stir until just combined. Fold in hazelnut meal. Pour mixture into pan.
4.Bake cake for 45 minutes or until a skewer inserted into the centre comes out clean. Leave cake in pan for 30 minutes.
5.Meanwhile, make vanilla bean cream. Scrape seeds from vanilla bean; reserve pods for another use (see tips). Place cream, vanilla seeds and sugar in a medium bowl; beat with an electric mixer until soft peaks form.
We used rapadura, but any unrefined sugar can be used.
The vanilla pods can be placed in a jar of sugar to make vanilla-flavoured sugar.
Cake will keep in an airtight container at room temperature for 3 days.