1.Process biscuits in a food processor until finely crumbed. Melt 125g of the butter. Transfer biscuit crumbs to a bowl and stir in melted butter. Press crumb mixture firmly over base and sides of a 23cm shallow flan tin and refrigerate while preparing the filling.
2.Place chocolate in a heat-resistant bowl with 1 tbsp of the coffee and remaining chopped butter. Place bowl over a pan of simmering water and stir until mixture is smooth and just melted. Remove bowl from heat and quickly beat in egg yolks with a wooden spoon. Cool 10 minutes.
3.Meanwhile, beat 150ml of the cream until soft peaks form. Fold cream into cooled chocolate mixture. Spread mixture into the crumb crust and refrigerate for several hours or until set.
4.Just before serving, beat remaining cream with the remaining coffee until soft peaks form. Spread coffee cream over pie filling, and dust lightly with sifted cocoa if desired.
Pie can be prepared a day ahead.Note