Preheat oven to 180º deg C.
Place butter and chocolate in saucepan and melt over very low heat, stirring until the mixture becomes just smooth.
Place eggs and sugar in a bowl and beat until pale and thick. Mix in Corn Flakes, flour and nuts with a wooden spoon, then fold in the chocolate mixture and pour into a 20 cm square cake tin, lined with baking paper.
Bake for 30 minutes or until firm to touch.
Allow to cool and dust with icing sugar.