Preheat the oven
to 180'C/350'F/Gas 4. Line and grease a 20cm/8in
loose-bottomed cake tin, add the sponge mixture and
bake for 20-25 minutes until firm and golden. Cool on
a wire rack, then split in half. Return the lower
half of the cake to the clean cake tin and set
aside.
Make the
filling. Whisk the egg yolks, sugar, lemon rind
and juice in a bowl until thick, pale and
creamy. In a greasefree bowl, whisk the egg
whites to soft peaks.
Sprinkle the
gelatin over the water in a bowl. When spongy,
dissolve over simmering water. Cool slightly, then
whisk into the yolk mixture. Fold in the fromage
frais. When the mixture begins to set, fold in a
generous spoonful of the egg whites to lighten it,
then fold in the remaining whites.
Spoon the lemon
mousse over the sponge in the cake tin. Set the
second layer of sponge on top and chill until set.
Carefully
transfer the cake to a serving plate. Pour the glace
icing over the cake and spread it evenly to the
edges. Decorate with the lemon shreds.