In a small bowl, combine 2 teaspoons confectioners’ sugar with 1 teaspoon cornstarch. Lightly grease a 9x9x2-inch pan and line it with parchment paper, allowing an overhang for easy removal. Grease the parchment and dust the surface evenly with the sugar-cornstarch mixture. Set aside.

Place ½ cup water in a small microwave-safe bowl. Sprinkle the gelatin over the water and stir briefly to combine. Set aside to allow the gelatin to bloom and absorb the liquid.

In a large saucepan, combine granulated sugar, corn syrup, ¼ cup water, and kosher salt. Cook over medium-high heat, stirring gently until the sugar dissolves. Continue heating until the syrup reaches 240°F (115°C) on a candy thermometer, or the soft-ball stage, approximately 5 minutes.

While the syrup cooks, microwave the gelatin mixture for 30 seconds until completely melted and smooth. Transfer the melted gelatin into the bowl of a stand mixer fitted with a whisk attachment.

With the mixer running on low speed, carefully drizzle the hot syrup into the melted gelatin, ensuring it runs down the side of the bowl to prevent splattering. Once all the syrup has been added, increase the mixer speed to medium and whip for 5 minutes. Then increase to medium-high and continue whipping for an additional 4 minutes, or until the mixture turns opaque, fluffy, and triples in volume. Add the peppermint extract and mix for one final minute.

Pour the marshmallow mixture into the prepared pan. Lightly wet your hands or a spatula and press the mixture evenly into the pan. Drop several small dots of red food coloring onto the surface and, using a toothpick, swirl the color decoratively throughout.

Allow the pan to rest uncovered in a cool, dry area for at least 8 hours or overnight until the marshmallows are firm to the touch.

In a large bowl, whisk together 4 tablespoons confectioners’ sugar and 2 tablespoons cornstarch. Lift the marshmallow slab from the pan using the parchment overhang and place it on a cutting board. Cut into 1½-inch squares, then coat each marshmallow in the sugar-cornstarch mixture to prevent sticking.

Store in an airtight container at room temperature for up to three weeks. Keep in a cool, dry environment and avoid refrigeration to prevent moisture absorption.