-
1
Combine the cornstarch and confectioners sugar and place in a fine-mesh sieve.
-
2
Generously dust the bottom of a large rimmed baking sheet (ideally a jelly-roll or half sheet pan about 13 by 18 inches) with about half of the mixture.
-
3
Set the remaining cornstarch mixture aside.
-
4
In a heavy-bottomed saucepan, combine the granulated sugar with 1 cup of the corn syrup and 3/4 cup of the water.
-
5
Clip a thermometer to the side of the pan, place the pan over medium-high heat, and heat, stirring occasionally, for about 15 minutes, or until the temperature registers 239F.
-
6
Meanwhile, put the remaining 1/2 cup water in the bowl of a stand mixer fitted with the whip.
-
7
Sprinkle the gelatin over the water and let stand, without stirring, for about 3 minutes to soften then add the remaining 1 1/4 cups corn syrup and beat on medium speed for about 4 minutes, or until frothy.
-
8
When the hot sugar mixture is ready, add it to the mixer bowl and beat on medium-high speed for about 5 minutes, or until medium peaks form or the mixture has reached its maximum volume.
-
9
Add the chocolate and whip just until combined.
-
10
Pour the mixture into the prepared pan, lightly coat an offset spatula with nonstick vegetable spray and lightly press on the mixture to spread it evenly.
-
11
Lightly and evenly dust the surface with the remaining cornstarchconfectioners sugar mixture by tapping on the side of the sieve.
-
12
Set aside to rest at room temperature for at least 8 hours or up to overnight.
-
13
Using a sharp knife, cut the sheet into 1-inch squares.
-
14
Layer the marshmallows, separated by waxed paper, in an airtight container at room temperature for up to 1 week.
