Line a 9×13 pan with parchment paper and lightly grease all over with vegetable oil or nonstick spray. Lightly dust with powdered sugar. In the bowl of a stand mixer, sprinkle gelatin over 1/2 cup cold water. Set aside.
Combine sugar, corn syrup, 1/4 cup water, and salt in a small saucepan fitted with a candy thermometer. Bring to a boil and boil hard, without stirring, until the temperature reaches 240°F (this took me about 20 minutes).
Turn the mixer on low and slowly pour the boiling syrup over the gelatin. Increase the speed to high and beat for 12 minutes or until the mixture is no longer expanding in volume. Add peppermint extract beat on high for another minute.
Pour the marshmallow into prepared pan. Pat the surface of the marshmallows with slightly damp hands until it is smooth and evenly spread throughout the pan. Randomly drop red food coloring over the surface and drag a sharp knife through the marshmallows to create a swirled pattern.
Let mixture sit, uncovered, for at least 12 hours at cool room temperature (or in the refrigerator if you live in a humid place like Bangkok).
Remove from pan, dust the marshmallows with powdered sugar and cut into 20-24 equal pieces with scissors or a chef’s knife. Dust each marshmallow with powdered sugar.
Store in an airtight container at room temperature for up to three weeks.