Cake: Preheat oven to 180 degrees C, Grease and line a 23cm springform cake tin.
In a large bowl beat the egg whites and salt until stiff.
In a separate bowl beat butter and Nutella together, then add Tia Maria, beaten egg yolks and ground hazelnuts. Gently fold in the melted chocolate, then lighten with a spoonful of egg whites. Then gently fold in the rest of the egg whites.
Pour mixture into the prepared cake tin and bake in the oven for 40 minutes or until it comes away from the sides of the tin.
Icing Toast hazelnuts in a dry frying pan until golden. Put the cream, Tia Maria and chocolate into a saucepan over a low-medium heat.
Once the chocolate has melted and combined with cream, remove from heat and allow to cool to a consistency whereby it can be spread over the top of the cake and not run down the sides.