Beat egg whites + 50g sugar until thick and firm.
In the same bowl, beat yolks + 50g sugar until creamy.
Add mascarpone to yolk mixture and blend until smooth.
Gently fold in the meringue (egg whites) using a spatula with a top-to-bottom motion.
Dip the biscuits quickly into the cooled espresso and layer them in a tray or make individual dessert bowls.
Cover each layer of biscuits with a generous amount of mascarpone cream.
Repeat layers and finish with a thick top layer of cream (this step is optional; the original tiramisu takes just one layer of biscuits, cream, and cocoa).
Cover and refrigerate for at least 4 hours or overnight.
Just before serving, sprinkle generously with unsweetened dark cocoa powder.
Store in the fridge for 2 to 3 days—flavor deepens beautifully over time.