Preheat the oven
to 160.C/325'F /Gas 3. Butter a 24cm/9Vrin
springform tin, sprinkle with sugar and tap out the
excess.
Set aside 45ml/3
tbsp of the sugar. Place the chocolate, butter and
remaining sugar in a heavy saucepan and cook over a
low heat until melted. Remove from the heat, stir in
the vanilla essence and leave to cool slightly.
Beat the egg
yolks, one at a time, into the chocolate mixture,
then stir in the flour.
Beat the egg
whites with the salt until soft peaks form. Sprinkle
over the reserved sugar and beat until stiff and
glossy. Beat one-third of the whites into the
chocolate mixture, then fold in the rest.
Pour the mixture
into the tin and tap it gently to release any air
bubbles.
Bake the cake for
35-45 minutes, until well risen and the top springs
back when touched lightly. Transfer to a wire rack,
remove the sides of the tin and leave to cool.
Remove the tin base, dust the cake with icing sugar
and transfer to a serving plate.