Place the espresso powder in a heatproof bowl with the boiling water, stir to dissolve and leave to cool slightly.
Place the mascarpone and icing sugar in a bowl and add the coffee. Beat using a hand-held electric whisk until smooth.
Whip the cream with a hand-held electric whisk until it forms soft peaks, then gently fold two-thirds of the cream into the coffee mixture. Divide the mixture between 6 espresso cups or small glasses, then top with the remaining cream.
Dust each portion with cocoa powder and decorate with a coffee bean. Serve immediately with the biscuits.