Step 1

Grease a 9x13-inch baking pan with cooking spray; dust with 1 tablespoon confectioners' sugar.

Step 2

Pour 1/2 cup lukewarm water into the bowl of a stand mixer fitted with the whisk attachment. Sprinkle 2 tablespoons plus 3/4 teaspoon gelatin on top; stir briefly to combine.

Step 3

Combine sugar, corn syrup, 1/2 cup water, and salt in a large saucepan. Cook over medium-low heat, stirring constantly, until sugar dissolves, about 5 minutes. Increase heat and cook, stirring constantly, until mixture registers 250 degrees F (121 degrees C) on a candy thermometer, about 5 minutes. Remove from heat.

Step 4

Turn the mixer on low speed and, while running, pour the hot sugar syrup in a thin stream down the side of the bowl. Increase speed to high and beat until marshmallow mixture is lukewarm and triples in volume, about 15 minutes. Mix vanilla extract.

Step 5

Pour marshmallow mixture into the prepared pan. Press into an even layer with wet hands. Dust with 2 tablespoons confectioners' sugar. Let stand at room temperature, uncovered, until set, 8 hours to overnight.

Step 6

Cut marshmallow mixture into desired shapes and toss in remaining 2 tablespoons confectioners' sugar.