Prepare the Gelatin – Sprinkle the gelatin over ½ cup of cold water in a mixing bowl and let it bloom for 5-10 minutes.
Make the Syrup – In a saucepan, combine sugar, corn syrup, salt, and the remaining ¼ cup of water. Heat over medium heat until the sugar dissolves, then bring to a boil and cook until it reaches 240°F (115°C) on a candy thermometer.
Whip the Mixture – Slowly pour the hot syrup into the bloomed gelatin while whisking on low speed. Increase to high speed and whip for 10-12 minutes until thick, glossy, and tripled in volume. Add cotton candy flavoring and food coloring, mixing until combined.
Set the Marshmallows – Pour the mixture into a greased and parchment-lined 9x9-inch pan. Smooth the top and let it set uncovered for 6 hours or overnight.
Cut and Coat – In a bowl, mix powdered sugar and cornstarch. Dust a cutting board with the mixture, turn out the marshmallows, and cut into squares. Toss each piece in the coating to prevent sticking.
