Homemade Marshmallows

Marshmallows aren't really jet-puffed. (who knew?) Instead, they're whipped light and fluffy by a hand beater then swirled with sugary-sparkles.

4 tbsp unflavored gelatin
2 cups sugar
1 tbsp light corn syrup
2 egg whites, room temperature
1 tbsp vanilla extract
¹⁄₂ cup confectioners' sugar
1 cup potato starch
colored sugar (for dusting)

Line a 9-by-13-inch pan with a piece of plastic wrap large enough to cover the bottom and sides and overhang the edges. Coat the wrap with cooking spray.
Combine gelatin with ³⁄₄ cup water in a bowl. Be sure the gelatin dissolves entirely and does not turn spongy. If necessary, microwave to keep it liquid while you prepare the rest of the recipe.
Combine sugar, corn syrup, and 1 cup water in a saucepan over medium heat until the sugar is completely dissolved. Continue cooking without stirring until the mixture comes to a boil.
Continue cooking until the mixture reaches 260°F, hard ball stage. While the mixture is cooking, place egg whites in the bowl of a stand mixer fitted with the whisk attachment. When the sugar syrup reaches 245°F, begin whipping the egg whites on medium-high speed until they form firm peaks.
When the sugar syrup has reached 260°F, remove from heat. Add the fully dissolved gelatin and swirl to incorporate.
With the mixer on low, pour the sugar syrup in a slow, steady stream into the egg whites; pour down the side of the bowl to prevent splattering.
Turn the mixer to high speed and whip for 3 to 5 minutes until the mixture is very thick and glossy white.
Stir in vanilla extract.
Use a rubber spatula to scrap the marshmallow into the baking pan. Smooth out the top and let it set overnight at room temperature.
When you are ready to cut the marshmallows, combine confectioners' sugar and potato starch into a bowl. Sprinkle some of the mixture over a clean counter. Turn out the marshmallow onto the surface and dust the surface and sides liberally to prevent sticking.
Using a sharp chef's knife, cut the marshmallow into cubes. Run the knife under hot water and wipe clean between cuts to prevent sticking and keep the cut edges neat.