Beat the egg yolks with the fructose to a smooth pale cream. Add mascarpone and vanilla extract mixing continuously.
The chocolate cream:
Melt the chocolate in a bain marie adding water and fructose. When cooled add the egg yolk and stir vigorously with a spoon.
Pour the vanilla cream in a bowl. Add the chocolate cream and stir delicately once or twice with a knife.
Put it in a freezer for at least 30 minutes.