Make coffee or espresso and allow to cool. Stir in coffee liqueur.
Heat dark chocolate in a microwave safe dish on 30 second intervals until melted. Allow to cool.
Whip egg yolks and sugar in a medium bowl until well blended. Bring a saucepan of water to a simmer and place bowl with egg yolks and sugar over saucepan. Water should just barely touch the bottom of the bowl.
Whip constantly, until egg yolk mixture reaches a temperature of 160 F. using a thermometer. Remove from heat and continue whisking another minute or two to cool egg yolks mixture. It should fall in thick ribbons when mixture is picked up with whisk.
Beat mascarpone until light, about 2 minutes.
Fold melted chocolate into egg yolks and sugar, then fold in mascarpone.
Dip each lady finger biscuit briefly into coffee. Don't soak them. Just 3 seconds on each side.
Lay the lady fingers on the bottom of an 8" or 9" springform pan, cutting biscuits to fit the curves of the pan.
Spread half of the chocolate mascarpone mixture over the biscuits, then repeat with the remaining biscuits and mascarpone.
Cover the top of the tiramisu with plastic wrap and refrigerate for several hours.
Just before serving, dust top of tiramisu with cocoa powder and chocolate shavings.