Step 1: Prepare the Coffee Mixture

1. Brew 1 ½ cups of strong coffee and let it cool to room temperature.
2. Add 1 tablespoon of sugar and 2 tablespoons of coffee liqueur (if using) to the coffee. Stir until the sugar dissolves. Set aside.

Step 2: Make the Cream Filling

1. Whisk Egg Yolks and Sugar: In a heatproof bowl, whisk together 4 egg yolks and ½ cup of sugar. Place the bowl over a pot of simmering water (double boiler method) and whisk continuously for 5-7 minutes until the mixture becomes pale, thick, and doubles in volume. Remove from heat and let it cool slightly.
2. Add Mascarpone: Once the egg yolk mixture has cooled, fold in 1 cup of mascarpone cheese until smooth and well combined.
3. Whip the Cream: In a separate bowl, whip 1 ½ cups of heavy cream with 1 teaspoon of vanilla extract until stiff peaks form.
4. Combine: Gently fold the whipped cream into the mascarpone mixture until fully incorporated. Be careful not to overmix.

Step 3: Assemble the Tiramisu

1. Dip the Ladyfingers: Quickly dip each ladyfinger into the coffee mixture, ensuring they are moist but not soggy. Arrange a layer of dipped ladyfingers at the bottom of an 8×8 inch (20×20 cm) dish.
2. Add the Cream Layer: Spread half of the mascarpone cream mixture evenly over the ladyfingers.
3. Repeat Layers: Add another layer of dipped ladyfingers, followed by the remaining cream mixture.
4. Chill: Cover the tiramisu with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and the dessert to set.

Step 4: Serve and Garnish

1. Dust with Cocoa: Before serving, dust the top of the tiramisu generously with unsweetened cocoa powder using a fine sieve.
2. Add Chocolate Shavings (Optional): For an extra touch of elegance, sprinkle dark chocolate shavings on top.
3. Slice and Serve: Use a sharp knife to cut the tiramisu into squares or rectangles. Serve chilled and enjoy!