Place the gelatin into the bowl of a stand mixer along with 1/2 cup of the water. This is called sponging. Have the whisk attachment standing by.

In a small saucepan combine the remaining 1/2 cup water, granulated sugar, corn syrup and salt. Place over medium heat until the sugar has dissolved. Do not let it boil at this stage.

Once the mixture reaches this temperature, immediately remove from the heat.

Turn the mixer on low speed and, while running, slowly pour the sugar syrup down the side of the bowl into the gelatin mixture. Once you have added all of the syrup, increase the speed to high. Continue to whip until the mixture becomes very thick and is lukewarm when you touch the bottom of the bowl, approximately 12 to 14 minutes. Add the vanilla during the last minute of whipping. While the mixture is whipping prepare the pans as follows.

Combine the confectioners' sugar and cornstarch in a small bowl. Lightly grease a 7 by 11-inch metal baking pan with flavorless oil. Sift the sugar and cornstarch mixture and move around to completely coat the bottom and sides of the pan. Return the remaining mixture to the bowl for later use.

Grease a spatula, and even your hands, believe me this is sticky stuff.

When the marshmallow are ready, work QUICKLY and scrape the mixture into the prepared pan, using your spatula for spreading evenly into the pan. Dust the top with enough of the remaining sugar and cornstarch mixture to lightly cover. Reserve the rest for later. Allow the marshmallows to sit uncovered for at least 4 hours and up to overnight.

Turn the marshmallows out onto a cutting board and cut a little smaller then your graham cracker using a pizza wheel or lightly oiled knife. Once cut, lightly dust all sides of each marshmallow with the remaining mixture, using additional if necessary.

Store in an airtight container for up to 3 weeks.