In the bowl of a stand mixer, combine 1/2 cup of the cold water and the gelatin. Stir until the gelatin is dissolved.
In a medium saucepan, combine the remaining 1/4 cup of cold water, the granulated sugar, light corn syrup, and salt. Stir until the sugar is dissolved. Bring the mixture to a boil over medium-high heat and continue to cook until the mixture reaches 240°F (115°C) on a candy thermometer.
Remove the pan from the heat and, with the mixer on low speed, slowly add the hot syrup to the gelatin mixture. When all the syrup has been added, increase the mixer speed to high and beat until the mixture is thick, white, and doubled in volume, about 12 minutes.
Add the vanilla extract and beat to combine.
In a small bowl, combine the powdered sugar and cornstarch. Grease an 8x8-inch baking pan with cooking spray. Sprinkle the sugar-cornstarch mixture evenly over the pan, then pour in the marshmallow mixture and spread it evenly. Sprinkle the top with more of the sugar-cornstarch mixture and let it sit uncovered for at least 6 hours, or overnight.
Turn the marshmallow out onto a cutting board and cut into 1-inch squares. Roll each square in the remaining sugar-cornstarch mixture to coat.
Interesting Facts
Marshmallows were originally made from the root of the marshmallow plant!
Marshmallows are very versatile and can be used in a variety of recipes, including s’mores, hot chocolate, and even savory dishes.
Marshmallows are a popular topping for ice cream sundaes.