Crush the biscuits in a bag with a rolling pin.
Melt the chocolate and butter together
and pour over the biscuits in a mixing bowl.
Mix
well, then use to line the
base and sides of a greased 23cm/9in
loose-bottomed flan tin or spring form tin. Leave to
chill.
For the filling, melt the chocolate in a
bowl set over a pan of simmering water
then remove from the heat and beat in the
Mascarpone cheese, egg yolks and brandy.
Lightly
whip the cream until just holding its shape and
gently fold in the chocolate
mixture.
Whisk the egg whites in a bowl
until standing in soft peaks. Add the caster sugar
a little at a time and whisk until thick and
glossy. Fold into the chocolate mixture, in 2
batches, until just mixed.
Spoon the mixture into the prepared base and
chill for at least 2 hours before
serving.