Preheat oven to 180°C (160°C fan-forced). Lightly grease a 21cm square baking pan and line with baking paper.
Place the dark chocolate and butter together in a medium saucepan over a very low heat, stirring until melted and smooth. Remove from heat and allow to cool for 10 minutes.
Place the eggs and sugar together in the bowl of an electric mixer and beat for 5 minutes or until light and fluffy. Slowly add the cooled chocolate mixture, beating until combined. Add the hazelnut meal, ¼ cup cocoa, baking powder and salt, folding gently until combined.
Pour mixture into the prepared baking pan and bake in preheated oven for 50 minutes. Remove from oven and allow to cool completely in tin for at least 4 hours, but preferably overnight, so the brownie sets.
Cut into 12 pieces. Serve brownies dusted with remaining cocoa.