In a bowl, whip the heavy cream and sugar together until soft peaks form.
Add the mascarpone cheese and coffee liqueur (if using) to the whipped cream and continue to whip until well combined and smooth.
Dip the ladyfingers quickly into the espresso, making sure not to soak them as they will become too soft.
Arrange a layer of espresso-soaked ladyfingers at the bottom of the dish.
Spread half of the mascarpone filling over the ladyfingers.
Add another layer of soaked ladyfingers on top of the mascarpone filling.
Spread the remaining mascarpone filling over the second layer of ladyfingers.
Sift the cocoa powder over the top to cover the tiramisu completely.
Cover with plastic wrap and chill in the refrigerator for at least 4 hours, or overnight to allow the flavors to meld.
Serve chilled, with additional cocoa powder dusted on top if desired.
