1/2 cup cocoa powder, divided
3/4 cup cold water, divided
2 tablespoons light corn syrup
2 (1/4-ounce) packets unflavored gelatin
3 large egg whites, at room temperature
1 teaspoon pure vanilla extract
1 1/4 cups sugar
4 ounce dark chocolate, chopped
pinch of kosher salt
1/4 teaspoon instant coffee granulate
Line an 8 by 8-inch baking sheet with parchment paper, sprinkle 2 tablespoons of cocoa powder on the bottom and the sides of the parchment paper, set aside.
In a microwave safe bowl, add chopped chocolate, salt and instant coffee, heat on high until chocolate is melted. Stop and stir at 30 seconds intervals. When chocolate is melted, stir in 1/4 cup cocoa powder. Set aside to let cool.
In a medium saucepan, add 1/3 cup of the water, the sugar and the corn syrup and heat over medium heat. Stir until the sugar dissolves. Once the sugar is dissolved, do not stir the mixture and continue to cook the syrup until it reaches 265 degrees F on the candy thermometer, about 8 to 10 minutes.
While the syrup is cooking, work on the gelatin and egg whites. In a microwave-safe bowl, sprinkle the gelatin over the remaining cold water and let it sit for about 5 minutes. Then heat the gelatin in a microwave for 25 to 30 seconds to liquefy it.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on medium-high speed until firm. As soon as the syrup reaches 265 degrees F, remove the pan from the heat. Transfer the syrup to a heat proof beaker with handle (I used my heat proof glass measuring cup. It’s safer and easier to control using a beaker to pour the hot syrup into the running mixer than pouring the hot syrup directly from the saucepan.)
With the mixer on medium low speed, slowly add the syrup to the egg whites. Pouring it between the spinning beater and the sides of the bowl. Add the gelatin and continue to beat for another 3 minutes. When the ingredients are fully incorporated and slightly cooled, beat in the vanilla and chocolate mixture until well combined.
With a rubber spatula, scrape the mixture onto the prepared baking sheet. Spread the mixture into the corners and smooth the surface. Dust the top of the marshmallow with the remaining 2 tablespoons of cocoa powder.
Leave it in a cool, dry place to set. It takes about 2 to 3 hours. Once the marshmallow is cooled and set, cut into small pieces with a pair of scissors or a long thin knife. I cut some of mine with cookie cutters. Lightly dust the cookie cutters with cocoa powder to prevent sticking. Eat them as is or add them into hot chocolate for a decadent treat. Enjoy.