Homemade marshmallows made with real vanilla bean have a soft, pillowy texture that store-bought versions rarely match. The process involves blooming gelatin, cooking a sugar syrup, and whipping everything together — plan for about 30 minutes of active work plus several hours of setting time.
Prepare the Gelatin Mixture: In the bowl of a stand mixer, combine 1/2 cup cold water and unflavored gelatin. Let it sit for about 10 minutes to bloom while you prepare the sugar syrup.
Make the Sugar Syrup: In a medium saucepan, combine granulated sugar, 1/4 cup cold water, light corn syrup, and kosher salt. Place over medium-high heat, attach a candy thermometer, and stir constantly until the sugar dissolves. Let the mixture boil until it reaches 240°F (116°C), without stirring, about 8-10 minutes.
Combine and Whip: With the mixer on low speed, carefully pour the hot sugar syrup into the gelatin mixture down the side of the bowl. Gradually increase the mixer speed to high and whip until the mixture is thick, fluffy, and lukewarm, about 10-12 minutes. Add vanilla bean seeds and vanilla extract during the last minute.
Prepare the Pan: While the marshmallow mixture is whipping, line an 8x8-inch baking dish with parchment paper and lightly spray with nonstick spray. In a small bowl, sift together powdered sugar and cornstarch, then generously dust the pan.
Pour and Set: Using a spatula, spread the mixture evenly in the prepared pan. Dust the top with the sugar-cornstarch mixture. Let it set for at least 4 hours or overnight, uncovered, at room temperature.
Cut and Coat: Turn the set marshmallow slab out onto a cutting board and peel off the parchment. Using a sharp knife dusted with cornstarch mixture, cut into squares. Toss pieces in extra powdered sugar-cornstarch mixture to prevent sticking.
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Notes
For a variation, replace vanilla bean with 1 teaspoon almond extract for almond-flavored marshmallows.