Step 1: Prep
Line a 9x9 pan with parchment paper and dust with Black Onyx Cocoa Powder. Add 1/2 cup cold water and gelatin to the bowl of a stand mixer. Whisk until smooth. Set bowl in stand mixer fitted with whisk attachment.
Step 2: Hot Sugar Syrup
To a medium pot, add corn syrup, Whiskey Barrel Smoked Sugar, and remaining 1/2 cup cold water. Place pot over medium-high heat and bring to a full boil. To prevent sugar crystals from forming, dip a pastry brush in water and occasionally brush down the sides of the pot. Do not stir the sugar once it has come to a boil or it may crystallize. Boil the syrup until it reaches 247°F to 250°F on a candy thermometer.
Step 3: Beat
Remove pot from heat and, with mixer on medium speed, carefully pour the hot sugar syrup down the side of the bowl into the gelatin. Increase mixer speed to high and whip marshmallow for 10 min. until thick and glossy and doubled in size. In the last minute, add Mexican Vanilla, Espresso Powder, Fine Pink Himalayan Sea Salt, and 1/4 cup Black Onyx Cocoa.
Step 4: Set
Pour mixture into prepared pan and let set 4 to 8 hours. Dust top of set marshmallow and the sides of a knife with Black Onyx Cocoa Powder. Cut marshmallows into 2x2 squares, dusting knife with Black Onyx Cocoa Powder as needed. Toss cut marshmallows in Black Onyx Cocoa Powder to prevent sticking.
Step 5: Assemble
Toast marshmallows over an open flame and sandwich with chocolate between 2 graham crackers.