Break the biscuits into rough pieces and divide between 4 coffee cups or glasses. Pour over the espresso.
Melt the chocolate in a heatproof bowl set over a pan of simmering water.
In a medium bowl, beat together the double cream, liqueur and mascarpone until smooth and creamy. Pour over the melted chocolate and stir a couple of times until rippled. Spoon over the top of the biscuits and serve.