Preheat oven to 170C
Melt the butter, chocolate and sugar together in a large pot on low heat.
Take off the heat as soon as it is melted and add the vanilla extract.
Whisk eggs in a jug. Mix in the eggs
Fold in dry ingredients
Fold in hazelnuts
Leave to cool in tin.
Once cool slice and dust with icing sugar.
Serve with coffee and tea