Whisk the egg yolks with the sugar using an electric mixer (or by hand) until pale and fluffy. No sugar grains should be felt if you rub the creamy mixture between your fingers. Gently mix in the mascarpone until smooth.
Using a clean whisk and a very clean bowl, whip the egg whites until white and stiff; adding a tablespoon of something acidic like lemon juice helps. In a circular move