from Alton Brown ©2007
3 packages unflavored gelatin
1 cup ice cold water, divided
1 1/2 cups sugar
1 cup light corn syrup
1/4 teaspoon kosher salt
1 teaspoon vanilla extract
1/4 cup powdered sugar
1/4 cup cornstarch
Place the gelatin into the bowl of a stand mixer with 1/2 cup of the water. Have the whisk attachment standing by.
In a small saucepan, combine the remaining 1/2 cup water, sugar, corn syrup and salt. Place over medium high heat, cover and allow to cook 3-4 minutes. Uncover, clip a candy thermometer onto the side of the pan and continue to cook until the mixture reaches 240°F, about 7-8 minutes, then immediately remove from heat.
Turn the mixer on low speed and, while running, slowly pour the sugar syrup down the side of the bowl into the gelatin mixture. Once all the syrup has been added, increase the speed to high. Continue to whip until the mixture becomes very thick and is lukewarm, about 12-15 minutes. Add the vanilla during the last minute of whipping. While the mixture is whipping, prepare the pan:
Combine powdered sugar and cornstarch in a small bowl. Lightly spray a 9 x 13 inch metal baking pan with nonstick spray. Add some of the cornstarch and sugar mixture and move around to completely coat the bottom and sides. Return remaining mixture to bowl for later use.
When ready, pour the marshmallow into the prepared pan, using a greased spatula to evenly spread the mixture. Dust the top with enough of the cornstarch and sugar to lightly cover. Reserve the rest for later.
Allow the marshmallow to sit uncovered for at least 4 hours or overnight.
Turn the marshmallow out onto a cutting board (if it is sticking, grasp a corner and gently pull it out) and cut into 1″ squares using a pizza wheel dusted with powdered sugar and cornstarch. Once cut, lightly dust all sides of the marshmallows with the rest of the cornstarch mixture.
Store in an airtight container for up to 3 weeks.