In a shallow dish, combine the cooled espresso, 1/4 cup granulated sugar, and coffee liqueur (if using). Stir until the sugar is dissolved. Set aside.

In a heatproof bowl (preferably from a stand mixer) combine the egg yolks. In a small saucepan, combine 3/4 cup granulated sugar and 1/4 cup water. Bring to a boil over medium heat, stirring until the sugar dissolves. Continue to boil without stirring until the syrup reaches 240°F (115°C) on a candy thermometer. If you don't have a thermometer, boil until it forms a soft ball when dropped in cold water.

With the stand mixer on medium-low speed (or using a hand mixer), slowly and carefully pour the hot sugar syrup in a thin stream into the egg yolks. Increase the speed to high and beat for 7-10 minutes, until the mixture is thick, pale yellow, and has tripled in volume. The bowl should be cool to the touch. This creates a safe, cooked sabayon base.

Reduce the mixer speed to low. Add the chilled mascarpone cheese, one spoonful at a time, mixing just until combined and smooth. Be careful not to overmix, or the mascarpone may curdle. Set aside.

In a separate large, chilled bowl, whip the cold heavy cream and vanilla extract with a clean whisk attachment (or hand mixer) on high speed until soft peaks form. Do not overbeat.

Gently fold the whipped cream into the mascarpone mixture in two additions using a spatula, until just combined and light. Do not overmix.

Dip each ladyfinger briefly into the espresso mixture (1-2 seconds per side). Do not over-soak, or they will become soggy. Arrange a single layer of dipped ladyfingers at the bottom of the 9x13 inch baking dish.

Spread half of the mascarpone cream evenly over the layer of ladyfingers.

Repeat with another layer of espresso-dipped ladyfingers, followed by the remaining mascarpone cream. Smooth the top with a spatula.

Cover the dish tightly with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow the flavors to meld and the tiramisu to set.

Before serving, use a fine-mesh sieve to dust a generous layer of unsweetened cocoa powder over the top of the Creamy Tiramisu.