In a medium heatproof bowl, whisk together the egg yolks and granulated sugar.
Place the bowl over a pot of simmering water (double boiler) and whisk constantly until the mixture becomes thick and pale, about 5-7 minutes. Remove from heat and let it cool slightly.
In a separate bowl, whip the heavy cream until stiff peaks form.
In another large bowl, combine the mascarpone cheese with the cooled egg yolk mixture, coffee liqueur (if using), and vanilla extract. Mix until smooth.
Gently fold in the whipped cream until fully incorporated.
In a shallow dish, combine the brewed coffee and any remaining coffee liqueur.
Dip each ladyfinger into the coffee mixture for about 2 seconds on each side, ensuring they are soaked but not soggy.
Arrange a layer of soaked ladyfingers at the bottom of a 9x13 inch (23x33 cm) dish or a similarly sized serving dish.
Spread half of the mascarpone mixture over the ladyfingers.
Repeat with another layer of soaked ladyfingers and the remaining mascarpone mixture.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow the flavors to meld and the dessert to set.
Before serving, dust the top of the tiramisu with unsweetened cocoa powder and sprinkle with dark chocolate shavings if desired.
Enjoy your meal!