Instructions:

1. Prepare the coffee. Add a teaspoon of sugar, stir until dissolved, and let the coffee cool completely.
   
2. Separate the egg yolk and egg white. In a bowl, whisk the egg yolk with the remaining sugar until light and creamy.
   
3. Add the mascarpone to the yolk mixture and mix until smooth and homogeneous.
   
4. In another bowl, whisk the egg whites with a pinch of salt until stiff peaks form.
   
5. Gently fold the whipped egg whites into the mascarpone mixture, taking care not to deflate the mixture. Fold until you have a smooth, airy cream.
   
6. Once the coffee is cool, dip each ladyfinger quickly into the coffee and arrange them in a dish to cover the bottom.
   
7. Spread a layer of the mascarpone cream over the ladyfingers.
   
8. Repeat steps 6-7 until all ingredients are used up.
   
9. Generously dust the top with unsweetened cocoa powder.
   
10. Refrigerate the tiramisu for at least 4 hours before serving.