Sift icing sugar into bowl, mix with hazelnuts.
Stir in just enough egg-white to make a firm paste; add cream.
Chop chocolate, place in top of double saucepan, stir over hot water until melted.
Blend into hazelnut mixture, stirring with wooden spoon; add rum.
Turn mixture into shallow tin lined with greased greaseproof paper; refrigerate until set.
When firm, cut into small squares, then roll into balls between palms of hands; roll in chocolate vermicelli.