Boil the icewine in a small saucepan for about 10 to 15 minutes, until reduced to a thick syrup. There should be about a 1/4 cup of syrup left.
Pour the 1/2 cup of cold water into the bowl of a stand mixer fitted with a whisk attachment. Sprinkle the gelatin over the water and let it stand for 10 minutes.
Meanwhile, mix the sugar, corn syrup, remaining water, and the icewine syrup. Bring to a boil and cook until the sugar reaches soft-ball stage (240ºF).
Turn on the stand mixer to a low setting. Slowly pour in the hot sugar mixture, allowing the sugar to run down the side of the bowl. Add the salt and turn up the mixer to the highest speed. Beat for 12 to 15 minutes, until the mixture is fluffy and soft. It should hold soft peaks. Add the vanilla and beat for a minute longer.
Pour the mixture into a 9 x 9-inch cake pan that has been greased with oil. Using slightly wet hands, flatten out the marshmallow. Allow to set for at least 2 hours in a cool dry area. (Do not place in the refrigerator.) Once the marshmallow is firm, remove from the pan. Cut into even squares and dust with confectioners’ sugar.
[Peeta’s note: Icewine or ice wine is a type of dessert wine produced from grapes that have been frozen while still on the vine. You can find it in most grocery and beverage stores. You can try other sweet dessert wines to give the marshmallows a different flavor]