Prepare a 12x8 baking dish (do not use a metal pan) by sprinkling it generously with powdered sugar. Set aside.
In the bowl of a stand mixer fitted with the whisk attachment combine the gelatin and ½ cup of cold water. Allow the mixture to sit.
In a large saucepan combine the sugar, corn syrup, and ½ cup water. Place over medium-high heat. Allow the sugar to dissolve and raise heat to high. Cook until the mixture reaches 240 degrees (F). Remove from heat.
Turn the mixer to low speed and slowly pour the sugar mixture down the side of the bowl into the gelatin.
Turn the mixer on high and allow to mix for about 15 minutes or until the mixture is very thick. Add the vanilla and combine.
Pour the mixture into the prepared pan, spread evenly, and dust the top with more powdered sugar.
Allow the mixture to sit overnight uncovered to allow the marshmallows to dry out.
Remove marshmallows from pan and cut into desired shapes.