Method
Melt chocolate in a bowl over simmering water, reserve some chocolate for decoration.
Whip the cream until fairly stiff.
Stir half the custard into the melted chocolate and the other half into the whipped cream with the vanilla essence.
Put a layer of the chocolate mixture into a serving dish followed by a layer of chocolate chip cookies that have been quickly "dunked" one by one into the sherry.
Cover the biscuits with a further layer of chocolate mixture followed by a layer of the cream mixture.
Continue with alternate layers, finishing with a cream layer.
Place into fridge until required.
Decorate the top with grated chocolate.