Oil a 9' heat proof baking tin or small casserole dish using a pastry brush. Sprinkle with icing sugar to coat entirely and knock out the excess. This step is very important as the marshmallow mixture is incredibly sticky.
Put 1/2 cup water in the bowl of a stand mixer fitted with a paddle attachment. Sprinkle the gelatin over top and give the mixture a stir. While the gelatin blooms, heat up the sugar, corn syrup, salt and water in a large sauce pan. Stir to dissolve the sugar. Heat the mixture to 240˚F and once reached, remove the mixture from heat and let stand until the bubbles subside.
Turn on the stand mixer to a low speed and carefully pour in the sugar mixture so that it runs down the side of the bowl. Once all the sugar syrup is in the bowl turn the mixer up the a high speed and beat for 2 minutes. The mixture will begin to grow in volume and look foamy. At this point add in the coffee granules. Continue to mix on high speed for another 6 minutes or until the paddle is lifted from the mixture and a thick ribbon of marshmallow falls back into the bowl.
Scrape the marshmallow into the prepared pan and let stand, uncovered at room temperature, until the surface is no longer sticky and you can gently pull the marshmallow away from the sides of the pan with your fingertips, at least 4 hours or overnight.
Dust a cutting board with icing sugar. Use your fingers to gently separate the sides of the marshmallow from the edge of the pan and invert onto the cutting board. Dust the top with icing sugar. Brush a long thin knife with vegetable oil and dust with icing sugar to prevent sticking; continue dusting the knife as necessary. Cut your marshmallow to match the size of your graham crackers.
Place one marshmallow between two graham crackers and dip one side into the chocolate. Let set completely in the fridge.