Weigh the eggs. Take the same weight in butter, sugar and flour. Beat the butter and sugar together until pale and light in texture. Wash the oranges and add the finely grated rind of 2 and the juice of 1 to the butter mixture. Mix the flour and baking powder and add alternately with the eggs. Beat thoroughly. Bake in a 24cm (91/2in) tin in a moderate oven, 180°C/350°F/gas 4, for 50 minutes approx. Cool the cake and split it in two. Sandwich with the orange butter icing and spread the chocolate icing over the top and sides allowing any excess to run off.