Preheat oven to 180°C. Grease and line a 2.5L gugelhupf pan.

Beat together the butter and sugar until pale. Add egg yolks, a little at a time, beating between each addition. Sift together flour and baking powder and fold into the egg mixture with the hazelnut meal and chocolate.

Beat the eggwhites in a clean bowl until soft peaks form. Fold 2 tablespoons of the eggwhite into the choc-hazelnut mixture to loosen, then fold in the remaining eggwhite until just combined. Pour into the pan and bake for 50-60 minutes, or untila skewer inserted into the centre comes out clean. Set aside to cool.

Melt the remaining chocolate in a bowl over a pan of simmering water. Drizzle over the cake and garnish with hazelnuts.