Spray a 9-inch square baking pan lined with parchment with cooking spray, and generously dust with confectioners’ sugar.

In a large bowl, place ⅓ cup (80 grams) water. Sprinkle gelatin over water, and let stand for 10 minutes.

In a large saucepan, combine granulated sugar, corn syrup, and remaining ⅓ cup (80 grams) water. Cook over medium-high heat until sugar is dissolved and a candy thermometer registers 240°F, about 6 minutes. Slowly drizzle sugar mixture into gelatin mixture, and beat in a stand mixer fitted with a whisk attachment at low speed just until combined. Increase mixer speed to medium, and beat until mixture begins to thicken, about 1 minute. Increase mixer speed to high, and beat until mixture turns very thick, white, and fluffy, about 10 minutes. Beat in vanilla bean powder. Spoon marshmallow mixture into prepared pan.

In a medium bowl, sift together confectioners’ sugar and cornstarch. Dust top of marshmallow mixture with confectioners’ sugar mixture, and flatten with hands. Let set for at least 2 hours or overnight.

Cut into pieces with a wet knife, and toss in confectioners’ sugar mixture. Store in an airtight container up to two weeks.