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Recipe adapted from Neil Robertson, Crumble & Flake, Seattle
Yield: 1 quarter sheet pan
Cook Time: 1 hour, 30 minutes, plus overnight refrigeration
¼ cup plus 1 teaspoon / 2¼ ounces / 65 grams cold water, divided
2 tablespoons / 1 ounce / 30 grams fresh lemon juice, divided
1½ teaspoons / ¼ ounce / 7 grams unflavored powdered gelatin (1 packet)
¾ cup / 5½ ounces / 150 grams granulated sugar
⅓ cup / 3½ ounces / 100 grams light corn syrup
Zest of 1 medium lemon
½ cup / 4 ¼ ounces / 120 grams cornstarch
½ cup / 2¼ ounces / 62 grams confectioners' sugar
1. Spray an 8-inch-by-8-inch baking pan or quarter sheet pan with nonstick cooking spray. In the bowl of a standing mixer, combine 1 tablespoon plus 2 teaspoons / ¾ ounces / 25 grams of the water and the lemon juice. Sprinkle the gelatin over the top and set aside for 5 minutes.
2. In a small saucepot set over high heat, combine the remaining 2 tablespoons plus 2 teaspoons / 1⅓ ounce / 40 grams of the water with the sugar and corn syrup. Bring the mixture to a boil and cook until the syrup reaches 240º on a candy thermometer, about 15 minutes. Remove the pan from the heat and set aside until the syrup cools to 200º, about 1 minute.
3. Using a standing mixer set on low speed, whisk the gelatin mixture for 10 seconds. With the mixer set to medium-high speed, carefully pour in the hot syrup, whisking until the mixture is very thick, fluffy and nearly cool, 8 to 10 minutes.
4. Add the lemon zest and whisk just to combine. Remove the bowl from the mixer and scrape the marshmallow into the prepared pan, spreading it into an even layer with an offset or rubber spatula (the marshmallow should be about an inch thick). Set aside, uncovered, at room temperature until firm and set, about 1 hour.
5. Spray the top of marshmallow lightly with cooking spray and cover with plastic wrap. Leave at room temperature or chill the marshmallow overnight (chilling makes cutting a little easier).
6. In a large bowl, whisk together the cornstarch and confectioners' sugar. Sift a few tablespoons of the cornstarch-sugar mixture over the top of the marshmallow and use your hands to lightly spread it into a thin, even coating. Carefully invert the marshmallow sheet onto a cutting board and sift a few tablespoons of the cornstarch-sugar mixture over the top side of the marshmallow. With a knife, pizza cutter or cookie cutter, cut the marshmallow into desired shapes and place the cut pieces in the bowl with the remaining cornstarch-sugar mixture, tossing to coat evenly. Transfer a few marshmallows to a fine-mesh strainer and shake gently to remove excess starch. Place in an airtight container and repeat with the remaining marshmallows. Store at room temperature for up to 3 weeks.