Melt the butter or margarine, sugar and syrup and stir in the biscuit
crumbs. Press into a 20 cm/8 in flan tin (pie pan) and bake in a preheated
oven at 180°C/350°F/gas mark 4 for 15 minutes. Chill until firm and crisp.
Melt the chocolate in a heatproof bowl over a pan of simmering water.
Remove from the heat and stir in the egg yolks and brandy. Leave to cool,
then fold in the cream. Whisk the egg whites until stiff, then fold them
into the mixture. Pour into the crumb case and chill until firm. Sprinkle
with the walnuts before serving.