Put the egg yolks in a stainless steel bowl. Whisk in the sugar, and Vin Santo wine or Marsala.
Bring water to a boil in a saucepan. Lower the heat and place the steel bowl over but not touching the water. Whisk the yolk mixture for 8 minutes, or until it becomes light and creamy. Monitor the heat, otherwise you'll end up with scrambled eggs. Set aside and let cool.
In another bowl, whip the cream with a hand mixer.
Gently fold the zabaione into the whipped cream with a rubber spatula, and place in the refrigerator for about 30 minutes, or until ready to serve. Serve in glasses with blueberries on top.
A good rule of thumb is a tablespoon of each ingredient per yolk.