Melt butter and chocolate, add crushed biscuits. Mix. Put in loose based flan tin (20cm), and press down. Chill.
Melt chocolate, add the 2 egg yolks. Mix .
Whisk the egg whites, until soft peaks form. Fold the egg whites into the chocolate mixture. Pour into tin . Chill.
Whisk egg whites until stiff. Add gran.sugar and whisk til stiff. Fold in caster sugar. Use to create a circle on baking tray. Bake 2 hours at 100c. Place on top of chocolate filling.