In a heatproof bowl, whisk together the egg yolks and sugar until pale and creamy.

In a saucepan, heat the milk until hot but not boiling. Gradually pour the hot milk into the egg yolk mixture, whisking constantly.

Return the mixture to the saucepan and cook over low heat, stirring constantly, until it thickens and coats the back of a spoon. Remove from heat and let it cool.

In a separate bowl, beat the heavy cream until soft peaks form. Add the mascarpone cheese and vanilla extract, and continue to beat until combined.

Gently fold the cooled custard into the mascarpone mixture until well incorporated.

In a shallow dish, combine the brewed coffee and coffee liqueur (if using). Dip each ladyfinger into the coffee mixture briefly, making sure not to soak them for too long, as they can become overly soft.

Arrange half of the soaked ladyfingers in a single layer in the bottom of a serving dish.

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

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld together and the ladyfingers to soften.

Before serving, dust the top of the tiramisu with cocoa powder.