1. Grease bottom and sides of a 9x9" baking dish and coat with confectioners' sugar, shaking out any excess; set aside. Stir together gelatin and 1/2 cup water in the bowl of a stand mixer fitted with a whisk and let sit until gelatin becomes very firm, about 10 minutes.
2. In a medium saucepan, combine granulated sugar, corn syrup, salt, and remaining 1/3 cup water over medium heat, stirring until sugar is dissolved. Bring to a boil and cook, without stirring, until mixture reaches 240 degrees on a candy thermometer, 8 to 10 minutes.
3. With mixer on low, carefully pour in hot syrup in a slow, steady stream. Increase speed to high and beat until mixture has tripled in volume and becomes very white and thick, 10 to 12 minutes. Add peppermint extract and beat 1 more minute.
4. Working quickly, use a greased rubber spatula to scrape marshmallow mixture into prepared baking dish and smooth top. Drop dots of food coloring evenly over top and, using a skewer, gently swirl to create a marbled pattern. Let mixture sit, uncovered, at room temperature until firm, at least 4 hours and up to overnight.
5. Dust cutting board liberally with confectioners' sugar. Loosen sides of dish with a knife, then invert marshmallows onto cutting board and dust with confectioners' sugar. Grease a chef's knife, dust with confectioners' sugar, and cut into 1 inch squares, re-dusting knife with more confectioners' sugar as needed. Working with one marshmallow at a time, coat all over with confectioners' sugar and shake off excess. Transfer to a resealable plastic bag or airtight container and store for up to 1 month.
Source: Hannaford fresh Magazine, November - December 2017