3 (.25-ounce) packages unflavored gelatin
1 1/2 cups sugar
1 cup light corn syrup
1/4 teaspoon kosher salt
2 teaspoons vanilla extract
1/4 cup powdered sugar
1/4 cup cornstarch
Cooking spray, as needed
In bowl of a stand mixer fitted with whisk attachment, combine the gelatin and 1/2 cup ice-cold water, set aside for about 10 minutes.
Meanwhile, in a medium saucepan, combine the sugar, corn syrup and salt with 1/2 cup ice-cold water. Place over medium-high heat, cover and cook for 3 to 4 minutes. Uncover, clip a candy thermometer onto side of pan and continue to cook (without stirring) until mixture reaches 240 F, about 6 to 8 minutes. Once mixture reaches this temperature, immediately remove from heat. Watch carefully: Do not let mixture brown at all; it should be clear.
Turn mixer on low speed and, while running, slowly pour sugar syrup down side of bowl into gelatin mixture. Once all syrup is added, increase speed to high. Continue to whip until mixture becomes very thick and lukewarm and increased in volume, about 12 minutes. Add the vanilla during last minute.
While mixture is whipping, lightly spray a 9-by-13-inch, metal baking pan with the cooking spray. Combine the powdered sugar and cornstarch in a small bowl. Shake some sugar-cornstarch mixture around to completely coat bottom and sides of pan. Reserve remaining mixture for later use.
Pour gelatin mixture into prepared pan, using a lightly oiled spatula to spread it evenly. Dust top with enough sugar and cornstarch mixture to lightly cover. Allow marshmallows to sit, uncovered, for at least 4 hours and up to overnight.
Turn marshmallows out onto a cutting board and cut into 1- to 2-inch squares using a lightly oiled pizza wheel. Once cut, lightly dust all sides of each marshmallow with remaining sugar-cornstarch mixture. Store in an airtight container for up to 3 weeks. Makes 30.
— Recipe adapted by the Detroit Free Press from www.foodnetwork.com