Pre-heat your oven to 150°C.
Line a cake tin with greaseproof paper.
Gently melt the chocolate and butter together over a bain marie.
Sieve together the flour and cocoa powder into a separate bowl.
In a large bowl whisk the eggs and sugar to ribbon stage, and then add to the chocolate.
Gently fold in the flour mix, and then add the hazelnuts.
Pour the mix into your prepared tin and bake for 25 minutes.
Serve with thickened cream, Chantilly or ice cream