Preparation

• Sift the confectioners’ sugar and cornstarch into a medium bowl.
• Generously coat the bottom and sides of a 9×13-inch baking pan (preferably one with straight sides) with cooking spray. Dust it well with about 1/4 cup of the sugar-cornstarch mixture, tapping any excess back into the bowl; set aside.
• Put 3/4 cup cold water in a small bowl, sprinkle the gelatin over the water, and stir until lump-free. Set aside to hydrate, at least 5 minutes.
• Put 1/2 cup cold water, the granulated sugar, and corn syrup in a 2- to 3-quart saucepan. If using a vanilla bean, split it and scrape the seeds into the pan; add the pod, too. Stir with a heatproof spatula just to combine (try not to get any sugar on the sides of the pan), then bring to a boil over medium-high heat without stirring. Attach a candy thermometer to the side of the pan.
• When the syrup reaches 240°F, begin beating the egg whites in a stand mixer fitted with the whisk attachment on medium speed until soft peaks form, 4 to 6 minutes. Turn the speed down to low.
• At this point, the syrup should be 250°F. If so, remove the vanilla pod, increase the speed on the mixer to medium low, and carefully pour the syrup down the side of the mixer bowl. (If not, turn the mixer off until the syrup reaches temperature and turn it on before adding the syrup.) With the mixer running, break the hydrated gelatin into several pieces and add it to the bowl one piece at a time, beating until incorporated. Increase the mixer speed to high and beat until the marshmallow is white, thick, and almost tripled in volume, about 6 minutes. If using vanilla extract, add it now, beating until just combined.
• Pour the marshmallow into the prepared pan, smoothing it into the corners with an offset metal spatula. Sift about 1/4 cup of the sugar-cornstarch mixture evenly over the top. Let set at room temperature for at least 3 hours and preferably overnight.
• Run the tip of a paring knife around the edge of the baking pan to loosen the marshmallow, and invert the pan onto a large, parchment-lined cutting board. Lift a corner of the pan and carefully free the corner of the marshmallow with your fingers, after which it will fall onto the board. Generously coat a sharp chef’s knife with cooking spray and cut the marshmallow into 1-inch pieces, respraying the knife as needed.
• Gently toss each marshmallow in the remaining confectioners’ sugar mixture to coat, shaking off the excess. Store the marshmallows in an airtight container at room temperature.

Make Ahead Tips

The marshmallows will keep in an airtight container at room temperature for up to 1 month.

Maple:Substitute pure maple syrup for half of the corn syrup.
Peppermint:Substitute peppermint extract for the vanilla extract; these are especially great for hot chocolate.
Cinnamon:Add a cinnamon stick to the syrup when you would add the vanilla bean; remove it when you would remove the vanilla bean. Before scraping the marshmallow mixture into the prepared pan, mix in 1/2 tsp. ground cinnamon.
Almond Crunch:用香草杏仁香精。年代后moothing the marshmallow mixture into the prepared pan, top with 1-1/2 cups toasted sliced almonds (instead of dusting with the sugar mixture). Once set, cut with the nuts on the bottom. Coat only the nut-free sides of the cut marshmallows in the confectioners’ sugar-cornstarch mixture.
Liqueurs:Swap out the vanilla extract with your favorite liqueur (we like Cointreau, Kahlúa, or framboise), starting with 1 Tbs.; we don’t recommend adding more than that because they’re not cocktails, ya know.

Marshmallow shapes:Big, fluffy cubes are great, but you can also pipe the marshmallow mixture into festive shapes or use holiday-themed cookie cutters. For piping, pour the finished marshmallow mixture into a pastry bag or large freezer bag and cut off the tip. Pipe rounds, stars, hearts, or anything you like onto a parchment-lined sheet pan. For cutting, oil tall metal or plastic cookie cutters and use them to punch out shapes; if your cutters have sides shorter than 1-1/2 inches, spread the finished marshmallow mixture into a larger pan. (And don’t forget to save the scraps for making s’mores or topping mugs of hot chocolate!)