Dice the butter into a large heat-proof bowl and break the chocolate in. Add the frangelico liqueur and set the bowl over a pan of simmering water. Stir until melted and then remove from the heat and leave to cool a little.
Meanwhile, separate the eggs, placing the whites into a large clean bowl and reserving the yolks. Whisk the whites until stiff.
Next, returning to the chocolate mixture, mix the sugar and ground hazelnuts through. Stir the egg yolks in, one at a time.
Finally, stir a spoonful of the whisked egg whites into the mixture and then very gently fold the remaining whites in until well blended.
This is delicious served with fresh raspberries & softly whipped cream or crème fraiche.