In the bowl of your stand mixer combine 1/2 cup of the water with the gelatin. Just pour the gelatin over the top of the water and let that sit while you do the next steps.
In a medium sized pot combine the remaining 1/2 cup water, sugar, corn syrup and salt over medium heat. Stir until dissolved. Turn the heat up and allow the mixture to reach 240°F. It is best to use a candy thermometer for this. Once the mixture reaches the desired temperature, remove from heat.
Turn your mixer (with the gelatin water) on low. If your mixer came with a splash guard, here's a good time to use it. ? Carefully pour the hot sugar mixture into the mixer while it's running. Pour in the peppermint extract. Now turn the speed up to medium/high and beat for about 6 minutes until the batter looks white and fluffy, like marshmallow cream.
In an 8×8 square pan, spray a thin coat of nonstick cooking spray, then sprinkle generously with powdered sugar. Add a couple drops of red food coloring if using. Pour a thin layer of marshmallow cream over the bottom of the pan. Use the edge of a knife to swirl the food coloring around. Pour the remaining marshmallow cream in, add a couple more dots of red food coloring and use your knife to swirl again over the top. Now sprinkle on some powdered sugar, cover and allow to set overnight.
The next day, plop the marshmallows out onto a cutting board. Use a pizza cutter to slice into squares. Store in an airtight container for up to two weeks.