Place the butter and sugar in a mixing bowl and beat
with a wooden spoon for about 10 minutes until pale
and fluffy. Gradually beat in the melted chocolate
until evenly mixed, then beat in the egg yolks.
Whisk the egg whites in a grease-free bowl until
stiff peaks form, then fold carefully into the
mixture, using a metal spoon. Carefully fold in the
sifted flour.
Pour the mixture into the prepared tin. Bake in a
preheated oven, 160°C (325°F), Gas Mark 3, for 1
hour until firm to the touch. Cool in the tin for 10
minutes, then turn the cake out on to a wire rack
and leave to cool completely before filling and
icing.
Split the cake in half and sandwich together with
half the jam. Brush the top and sides with the
remaining jam. Melt the plain chocolate in a bowl
set over a saucepan of hot water, and then remove
from the heat and stir in the milk. Pour the
chocolate evenly over the cake, using a palette
knife to coat the sides. Leave to set completely.
Melt the milk chocolate in a heatproof bowl set over
a pan of gently simmering water. Place in a grease
proof paper piping bag fitted with a thin writing
nozzle. Pipe the word 'sacher' in flowing writing
over the cake.
Decorate with a few sugar flowers,
attaching them to the cake with dabs of melted
chocolate so that they adhere firmly to the
chocolate icing.