Melt chocolate and rum over hot water. Cool, do not allow to set. Cream butter and sugar until light and fluffy, add egg yolks gradually. Beat well. Transfer mix to large bowl. Stir in chocolate mix and almonds. Beat egg whites until firm peaks form. Add extra sugar. Beat until dissolved. Fold egg whites and sifted flour gradually into chocolate mix. Spread into well-greased deep round cake tin which has base lined with greased, grease-proof paper. Bake in moderate oven (350 degree) 50 minutes. Stand five minutes before turning onto wire rack to cool. When cold, spread top and side with chocolate icing. Toast flaked almonds five minutes in moderate oven and cool. Press toasted, flaked almonds around top and side. Icing: Melt chocolate, butter, and rum together over hot water. Stir till smooth. Cool until thick and spreadable.