Put the gelatin and ½ cup of the cold coffee into the bowl of a stand mixer, with the whisk attachment. Set aside.

Combine the other ½ cup of coffee, white sugar, corn syrup and salt in a medium saucepan, and cook, covered over medium-high heat for 3-4 minutes. Remove the lid and clip a candy thermometer onto the side of the pan and continue cooking until the mixture reaches 240 degrees F, approximately. Once the mixture reaches this temperature, take it off the heat.

With the mixer running on low speed, slowly pour the hot sugar syrup mixture down the side of the stand mixer bowl into the gelatin mixture. Then increase the speed to high. Continue to whip until the mixture becomes very thick and is lukewarm, about 12 to 15 minutes. Add the vanilla, and 2 tablespoon of cocoa powder during the last minute of whipping.

While the mixture is whipping prepare the pans as follows: Combine the powdered sugar, corn starch, and 2 tablespoon of cocoa in a small bowl. Lightly spray a 9 by 9-inch baking pan with nonstick cooking spray. Add ¼ cup the powdered sugar mixture and move around to completely coat the bottom and sides of the pan. Return the remaining mixture to the bowl for later use. When ready, pour the marshmallow mixture into the prepared pan, using a lightly oiled spatula for spreading evenly into the pan. Dust the top of the marshmallows with more of the powdered sugar mixture to lightly cover, save the rest for later.A

llow the marshmallows to sit uncovered for at least 4 hours and up to overnight at room temperature.

Turn the marshmallows out onto a cutting board and cut into 1-inch squares using a pizza cutter dusted with the icing sugar mixture, or a sharp knife. Once cut, lightly dust all sides of each marshmallow with the remaining powdered sugar mixture. Store in an airtight container for up to 3 weeks.