1. Prepare the Crust:

1. Prepare a 9×9 inch pan by lining it with parchment paper and spraying it with non-stick cooking spray. In the bowl of a stand mixer, sprinkle the gelatin over 1/2 cup of the ice cold water.
2. In a medium saucepan, combine the remaining 1/2 cup water, granulated sugar, corn syrup, and salt. Heat over medium heat, stirring until the sugar dissolves. Then, stop stirring and cook until the mixture reaches 240°F (115°C) on a candy thermometer.
3. With the mixer on low speed, carefully pour the hot sugar syrup into the gelatin mixture. Gradually increase the speed to high and whip for 10-12 minutes, until the mixture is very thick and fluffy.
4. Add the vanilla and peppermint extracts and whip for one more minute to combine. Drop small dots of red food coloring across the surface of the marshmallow fluff. Use a spatula to gently fold and swirl the color 2-3 times; do not overmix.
5. Pour the marshmallow mixture into the prepared pan. Let it sit, uncovered, for at least 4 hours or overnight until firm.
6. Whisk together the powdered sugar and cornstarch. Sift this mixture over a cutting board. Turn the set marshmallow slab out onto the board and cut it into squares with a sharp knife. Toss each marshmallow in the sugar-cornstarch mixture to coat all sides.