Step 1: Prepare Espresso Mixture

• In a shallow dish, combine the cooled coffee and coffee liqueur (if using).
• Set aside.

Step 2: Make Mascarpone Filling

• In a large mixing bowl, beat the egg yolks with 1/2 cup of sugar until pale and thick.
• Add the vanilla extract and mascarpone cheese to the egg yolk mixture. Beat until smooth and creamy.
• In a separate bowl, whip the heavy cream until stiff peaks form.
• Gently fold the whipped cream into the mascarpone mixture until well combined.

Step 3: Assemble Tiramisu

• Dip each ladyfinger cookie into the coffee mixture briefly, ensuring they are soaked but not overly soggy.
• Arrange a layer of soaked ladyfingers in the bottom of a 9×9-inch dish.
• Spread half of the mascarpone filling over the ladyfingers, smoothing it out evenly.
• Repeat with another layer of soaked ladyfingers and the remaining mascarpone filling.
• Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight, to allow the flavors to meld and the tiramisu to set.

Step 4: Serve

• Before serving, dust the top of the tiramisu with unsweetened cocoa powder for a finishing touch.
• Slice into portions and serve chilled.