Using vegetable oil, brush the bottom of a 9-inch baking pan. I recommend a square pan. After, dust your pan using confectioner's sugar.In the bowl of a standing mixer add 1/2 cup of water and 2 gelatin packages. Mix and set aside.
In a large saucepan, combine the corn syrup, salt, 1/2 cup water and granulated sugar. Place over medium heat. Bring to a boil. Stir the sugar until it has dissolved. Place the candy thermometer into the syrupy liquid -- without stirring -- until it is at 240°F.
While the mixer runs on low speed pour the hot sugar mixture into the bloomed gelatin. Gradually increase mixer speed to high. Beat until the marshmallow has a very thick consistency. You will know it's ready when it forms a thick ribbon once the whisk has been removed. Mix in the vanilla once the desired consistency is reached.
Transfer the marshmallow to the pan. WARNING: It will be sticky. You can use a spatula or wet your fingers to spread the marshmallow evenly and smooth the top. Allow it to sit, uncovered at room temperature for at least 4 hours.
Dust the cutting board using confectioner's sugar. Use a spatula to gently pull the marshmallow from the pan's sides and bottom. Place the marshmallow on the cutting board and dust the top with confectioner's sugar. Cut the marshmallow into the desired number of pieces dusting the knife between each cut. Dust the cut sides of marshmallows with confectioner's sugar s they don't stick together.