Preheat the oven to 180C/365F/Gas 4.
Mix the biscuits and melted butter together in a bowl. Press the mixture into the base and sides of a 23cm/9in springfrom tin. Chill in the fridge for 10 minutes.
For the filling, melt the chocolate and butter together in a heatproof bowl set over a pan of simmering water. (Do not let the base of the bowl touch the water).
Meanwhile, whisk the eggs and sugar together in a bowl for 5-6 minutes, or until thick and creamy. Fold in the cream and melted chocolate mixture. Pour into the chilled springform tin and bake in the oven for 40-50 minutes, or until just set. Remove from the oven and set aside to cool completely.
Meanwhile, for the fudge sauce, heat all of the fudge sauce ingredients in a saucepan, stirring regularly, over a medium heat until the mixture is smooth and glossy. Set aside to cool for 5 minutes.
Spread the sauce over the cooled pie and chill in the fridge for 20 minutes. Serve with double cream.