Add half the sugar to the egg yolk, and beat with a whisk. When the mixture is creamy, slowly add the mascarpone cheese.
In another bowl whisk the egg whites with the sugar until stiff. Add the beaten egg white to the cream with the mascarpone.
In a baking dish spread 2 spoons of the cream. Dip the ladyfingers in the coffee and start distributing them evenly onto our bed of cream.
In the last layer dust the tiramisu with sifted cocoa.