Follow these step-by-step instructions to create the perfect tiramisu:

Step 1: Prepare the Espresso Mixture

1. Brew a strong espresso and let it cool to room temperature.
2. If using coffee liqueur, add it to the espresso and mix well. This will enhance the coffee flavor and add depth to the dessert.

Step 2: Make the Mascarpone Cream

1. In a large mixing bowl, whisk together the egg yolks and granulated sugar until the mixture is pale and creamy.
2. Add the mascarpone cheese to the egg mixture and gently fold it in until smooth and well combined.
3. In a separate bowl, whip the heavy cream and vanilla extract until stiff peaks form.
4. Carefully fold the whipped cream into the mascarpone mixture, ensuring it remains light and airy.

Step 3: Assemble the Tiramisu

1. Dip each ladyfinger briefly into the espresso mixture, ensuring they are soaked but not overly saturated.
2. Arrange a layer of soaked ladyfingers at the bottom of a 9×13-inch dish.
3. Spread half of the mascarpone cream mixture evenly over the layer of ladyfingers.
4. Add a second layer of soaked ladyfingers on top of the mascarpone cream.
5. Spread the remaining mascarpone cream over the second layer of ladyfingers.

Step 4: Chill and Serve

1. Cover the tiramisu with plastic wrap and refrigerate for at least 4 hours, preferably overnight. This allows the flavors to meld and the dessert to set properly.
2. Before serving, dust the top with cocoa powder and garnish with dark chocolate shavings, if desired.