Grease and line the bases of two 20 cm/8 inch round
sandwich tins. Put the eggs and sugar in a large
heatproof bowl over a pan of simmering water and whisk
until the mixture is thick enough to leave a trail when
the whisk is lifted from the bowl. Remove from the heat
and whisk until cool.
Sift the flour into the bowl. Add the grated chocolate and
fold in using a large metal spoon.
Turn
into the prepared tins and bake in a preheated oven,
180°C
(350°F), Gas Mark 4, for 20-25 minutes until just firm.
Transfer to a wire rack to cool.
Stir the rosewater into
the crème fraiche and use to sandwich the two cakes
together on a serving plate.
Put the white chocolate and
butter in a heatproof bowl over a pan of gently
simmering water and leave until melted. Stir in the
cream and icing sugar, and beat until smooth.
Leave
the mixture to cool until it forms soft peaks, then
spread it over the top and sides of the cake using a
palette knife.
Decorate the top of the cake with grated white chocolate
and a light dusting of icing sugar.