Put the chocolate, Nutella, sugar and butter in a big saucepan and melt slowly over a very low heat, stirring occasionally. Remove from the heat and stir in the ground hazelnuts, then egg yolks, one at a time. Whisk the mixture well until smooth.
Scrape the mixture gently into the pan and sprinkle the chopped hazelnuts on top. Bake for 40-45 minutes until a toothpick inserted into the center comes out with moist crumbs. Allow to cool completely on a wire rack, then refrigerate for at least 6 hours until completely set.
To serve, remove the cake from the pan, using a knife to loosen the sides, and dust with cocoa powder if you like. I recommend cutting the cake into thin slices because it’s very rich.
Recipe comes from Olive Magazine