Mix cocoa powder into cooled espresso and place it in a deep plate.
Dip ladyfingers into espresso, arranging them tightly in a 9x9" pan.
Cover with half of the mascarpone cream and spread evenly.
Pour half of the ganache and spread it.
Repeat the process for another layer.
Cover and refrigerate for at least 4 hours, ideally overnight.
Dust with cocoa powder before serving.