Separate the eggs into two bowls.
Whisk the egg whites until nice and fluffy.
Whisk the yolks with the sugar, mascarpone and yoghurt until smooth.
Fold the whites into the yolk mixture.
Squeeze the lemons into a separate bowl and stir in some sugar and Limoncino to taste
Dip half of the sponge fingers one at a time into the lemon juice for a second or two (not so long that they fall apart!) and arrange in the serving dish.
Spoon over half of the marscapone mixture
Repeat with the other half of the sponge fingers, dipping in the lemon juice and arranging in the serving dish.
Spoon over the rest of the marscapone mixture and level.
Grate over white chocolate to finish.
Allow to chill and set somewhat in the fridge for a couple of hours