Put the espresso/coffee in a shallow bowl and set aside.
Add the egg yolks and half of the granulated sugar in a bowl and whip it with an electric mixer until very pale yellow and smooth.
Place the mascarpone in a bowl and work it a bit with a fork to make it softer. Then add in the egg yolk mixture and mix it in softly.
Add the egg whites in a clean bowl and whip them for a couple of minutes with an electric handmixer on low speed until they start to foam. Then turn the handmixer on high speed ad, while mixing, the rest of the sugar one tablespoon at a time. Make sure the sugar is dissolved before you add another tablespoon. The egg whites are ready once they have stiff peaks and are shiny.
Combine the egg whites and mascarpone mixture. Mix them together, very gently! Otherwise you will beat all the air out of it.
Dust the bottom of a dish with 1 tablespoon cocoa powder.
Working one at a time, quickly dip each ladyfinger into the espresso - they are quite porous and will fall apart if left in the liquid too long - and place them at the bottom of the dish. Repeat, using half the ladyfingers, until you’ve got an even layer, breaking the ladyfingers in half as needed to fill in any obvious gaps (a little space in between is O.K.). Spread half the mascarpone mixture onto the ladyfingers in one even layer. Shave the dark chocolate in an even layer until the mascarpone mixture is covered.
Repeat with remaining espresso-dipped ladyfingers and mascarpone mixture.
Dust the top layer with the remaining cocoa powder. Top with shaved or finely grated chocolate.
Leave the Tiramisu for at least an hour in the refrigerator before indulging. Enjoy!