Step 1: Prepare the Coffee Mixture

• Brew a strong cup of coffee and let it cool to room temperature.
• Add the dark rum or coffee liqueur if desired, then pour the coffee mixture into a shallow dish for dipping the ladyfingers.

Step 2: Make the Mascarpone Cream

• In a mixing bowl, beat the egg yolks and caster sugar until pale and creamy.
• Add the mascarpone cheese and vanilla extract (if using), then beat until smooth and well combined.

Step 3: Whip the Egg Whites

• In a separate clean bowl, whisk the egg whites until they form soft peaks.
• Gently fold the whipped egg whites into the mascarpone mixture, using a spatula to keep the mixture light and airy.

Step 4: Layer the Tiramisu

• Quickly dip each ladyfinger biscuit into the coffee mixture, just enough to soak but not too soggy.
• Arrange a layer of coffee-dipped ladyfingers at the bottom of your serving dish or pan.
• Spread half of the mascarpone mixture over the ladyfingers, smoothing it with a spatula.

Step 5: Repeat the Layers

• Add another layer of coffee-dipped ladyfingers on top of the mascarpone layer.
• Spread the remaining mascarpone mixture evenly over the second layer of ladyfingers.

Step 6: Dust with Cocoa Powder

• Using a fine sieve, dust the top layer of mascarpone with cocoa powder for a rich, chocolatey finish.

Step 7: Chill and Serve

• Cover the tiramisu with plastic wrap and refrigerate for at least 4 hours (or overnight) to let the flavors meld.
• Before serving, add a fresh dusting of cocoa powder or garnish with chocolate shavings if desired.