Put a layer of finger biscuits at the bottom of a dish.
Gently pour coffee over the biscuits, until the biscuits are soft but there is no excess coffee floating in the dish.
Separate the eggs into two bowls: whites in one, and yolks in the other.
Add the sugar to the egg-whites and using an electronic whisk, beat until the mixture is firm and you can tip it upside-down without it falling out of the bowl.
Add the mascarpone to the egg yolks and use a hand whisk to mix them together, until there are no lumps.
Gently fold the egg whites into the yolks and mascarpone, one spoonful at a time. Repeat until there are no lumps.
Pour the mascarpone mixture over the finger biscuits.
Place in the fridge for at least 4 hours, or until the mix has set.
Dust with cocoa powder to serve.