For this recipe, you'll need a candy thermometer, in addition to the ingredients listed below.
Ingredients
¼ cup cornstarch
¼ cup powdered sugar
1 cup water, divided
4 packets (3 tablespoons) unflavored gelatin
¾ cup light corn syrup
¼ teaspoon salt
2 cups white granulated sugar
2 tablespoons vanilla
Instructions
Line a 13x9 inch pan with aluminum foil and spray with cooking oil. Combine the cornstarch and powdered sugar, and dust the coated pan. Tap excess into a small bowl and set aside for dusting the marshmallow tops.
In a large bowl, or the bowl of a stand mixer, sprinkle 3 tablespoons (4 packets) unflavored gelatin over ½ cup cold water, set aside. This will "bloom" or solidify as the sugar mixture is prepared.
In a medium saucepan, pour corn syrup and ½ cup water. Add the sugar and salt to the center of the pan.
Bring mixture to a boil over medium heat, swirling the pan occasionally (do not stir). When the mixture is 240-244 degrees fahrenheit on a candy thermometer ("soft ball" stage), remove from heat.
Start the stand or hand mixer on a slow speed, breaking up the gelatin. Add the hot sugar syrup in a slow but steady stream.
Beat mixture on "high" for 12-15 minutes, or until the mixture is white, glossy, fluffy, and stiff, but still warm.
Using a greased or oil-sprayed spatula, transfer the marshmallow mixture into the prepared pan. Tap the pan a few times--air bubble should rise to the top of your mixture, though they may not pop.
Allow mixture to set until cooled completely, at least 6 hours.
Using the reserved cornstarch/powdered sugar, dust your work surface and the top of the set marshmallows. Turn the marshmallow out onto a cutting board or work surface.
Cut into cubes with greased kitchen shears or a greased chefs knife before tossing in powdered sugar (to prevent sticking). Marshmallows will keep in an airtight container, at room temperature, for up to a week (though they rarely last that long).
Recipe by Laughing Over Spilled Milk at https://www.laughingoverspilledmilk.com/homemade-marshmallows/