Lightly grease a quarter sheet tray (9 by 13 inches) with nonstick spray. Line with parchment paper and spray the parchment with nonstick spray. Have an offset spatula and a heat-safe Silicone spatula ready, both sprayed with nonstick spray.
Pour 1/4 cup of the water in a small bowl and sprinkle the gelatin on top. Allow to bloom for 5 minutes undisturbed. It’s best not to stir, as the gelatin can form globs, and some of the gelatin on the interior of a glob may not come in contact with water, which can lead to an unpleasant graininess in your end product. The gelatin should be fully hydrated —no visible dry granules.
In a small pot, combine the remaining 1/4 cup water, sugar, corn syrup, and vanilla. Heat the pot over medium-high heat. Stir the mixture until it comes to a boil, then stop stirring completely: Agitating a boiling sugar syrup can encourage crystals to form, which can lead to disaster. Once you stop stirring, brush any visible sugar crystals away from the sides of the pot with a damp pastry brush.
Once the mixture begins to boil, fasten a candy thermometer to the side of the pot. Continue to boil until the temperature reads 245° F.
Pour the syrup into the bowl of an electric mixer fitted with the whisk attachment. Add the vanilla and let the mixture cool to 220° F.
While the syrup cools, melt the bloomed gelatin, either in the microwave (15 to 20 seconds) or over a double boiler, until it is fluid.
When the sugar syrup has cooled, gradually working your mixer up to medium speed. Once the mixer is running, add the melted gelatin (and any extracts, if using).
Whip the sugar on medium speed until the bowl feels almost entirely cool to the touch and the sugar is opaque white and very fluffy, 4 to 5 minutes. It should hold stiff peaks. Try not to stop and restart the mixer multiple times, just keep whipping steadily for 4 to 5 minutes.
Pour the marshmallow into the prepared pan, using the greased Silicone spatula to help you get it out of the mixer bowl. Working quickly, use the greased offset spatula to spread the marshmallow into an even layer inside the pan. You must work fast because as the mixture cools, the gelatin is setting.
Let the mixture cool completely inside the pan, at least 45 minutes and up to overnight (if you leave it overnight, cover the surface with greased plastic wrap).
Fill a large, shallow bowl with confectioners' sugar. Grease the blades of kitchen shears with nonstick spray and cut the marshmallow into 1-inch wide strips.
Holding each strip over the bowl of confectioners' sugar, cut into 1 inch wide squares, letting the pieces fall into the sugar. Toss each piece in confectioners' sugar to coat and repeat until all pieces are cut and coated.
Store finished marshmallows in an airtight container at room temperature. Add some extra confectioners’ sugar to the storage container to keep the 'mallows in a sugar bath at all times. They should last for up to 3 weeks at room temperature. Like many candies, the enemy of marshmallows is moisture, including humidity. Prolonged exposure to heat can also make them melt or otherwise deteriorate.
I always carry three kinds of hot sauce in my purse. I have a soft spot for making people their favorite dessert, especially if it's pie. My first cookbook, The Fearless Baker, is out on October 24, 2017.