In a shallow dish, combine the brewed coffee and coffee liqueur (if using). Set aside to cool completely.

In a large mixing bowl, whisk the egg yolks and granulated sugar together until the mixture is pale and creamy, about 5 minutes.

Add the mascarpone cheese to the egg yolk mixture and gently fold until smooth and well combined.

In a separate bowl, whip the heavy cream and vanilla extract until stiff peaks form. Carefully fold the whipped cream into the mascarpone mixture until fully incorporated.

In another bowl, beat the egg whites until stiff peaks form. Gently fold the egg whites into the mascarpone mixture, being careful not to deflate the mixture.

Quickly dip each ladyfinger into the coffee mixture, ensuring they are soaked but not soggy. Arrange half of the soaked ladyfingers in a single layer in a 9x9-inch dish.

Spread half of the mascarpone mixture over the ladyfingers. Repeat the process with the remaining ladyfingers and mascarpone mixture.

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.

Before serving, dust the top with unsweetened cocoa powder and garnish with dark chocolate shavings if desired.