In a bowl (that can fit ladyfingers), prepare your brewed coffee. I use instant coffee in this case, but you can also use espresso. Set aside to cool.
In a metal bowl, place egg yolks, powdered sugar, and 1 tbsp rum. Whisk until combine.
Place it on top of a bowl of hot water. Continue to whisk until the mixture is pale and thick. This process takes around 5 minutes.
Remove the yolk mixture from the hot water bath, and add mascarpone cheese.
Whisk the mascarpone mixture until creamy and soft.
In the cool-down brewed coffee, add 1 tbsp rum. Mix until combine.
One at a time, dip the ladyfingers on both sides quickly into the coffee mixture and arrange in an even layer in the bottom of a glass container. (I use my glass lunch box – 20cm*15cm)
Spread half the filling over the ladyfingers, and repeat.
Spread the rest of the filling on top and refrigerate for at least 4 hours, but preferably overnight. I recommend using the airtight glass container with a lid. Otherwise, make sure to cover your tiramisu with plastic wrap before placing it in the fridge.
Dust cocoa powder before serving.