1. Prepare the Pan:

• Line a 9×9-inch (23×23 cm) baking pan with parchment paper. Lightly grease it with cooking spray or a thin layer of oil.

2. Bloom the Gelatin:

• In the bowl of a stand mixer, combine 1/2 cup of cold water and the gelatin. Let it sit for 5–10 minutes to bloom.

3. Cook the Sugar Syrup:

• In a medium saucepan, combine the granulated sugar, corn syrup, salt, and the remaining 1/4 cup of water.
• Heat over medium heat, stirring until the sugar dissolves. Increase the heat to medium-high and bring to a boil. Cook until the mixture reaches 240°F (115°C) on a candy thermometer.

4. Whip the Marshmallow Mixture:

• Turn the mixer on low speed and carefully pour the hot sugar syrup into the bloomed gelatin. Gradually increase the speed to high and beat for 10–12 minutes, or until the mixture is thick, fluffy, and slightly cooled.
• Add the cotton candy flavoring and a few drops of food coloring. Mix until evenly combined.

5. Transfer to the Pan:

• Pour the marshmallow mixture into the prepared pan. Smooth the top with a greased spatula. Let the marshmallows sit at room temperature for 6–8 hours, or overnight, to set.

6. Cut and Coat the Marshmallows:

• In a small bowl, mix the powdered sugar and cornstarch. Dust a work surface with the mixture.
• Turn the marshmallow slab out onto the surface, peel off the parchment paper, and dust the top with the powdered sugar mixture.
• Use a greased knife or cookie cutters to cut the marshmallows into squares or shapes. Toss the cut marshmallows in the powdered sugar mixture to coat.

7. Serve and Enjoy:

• Store in an airtight container at room temperature for up to 1 week.