Combine the chopped chocolate and coconut oil in a medium heatproof bowl and place over a medium saucepan of barely simmering water (with the bowl not touching the water).
Heat, stirring occasionally until the mixture is fully melted and combined.
Remove from the heat and let cool to room temperature.
Chocolate Graham Crackers:
Preheat the oven to 325°F (162°C) with racks in the upper and lower thirds of the oven. Line three baking sheets with parchment paper.
Sift the flours, cocoa powder, sugar, and baking powder in a food processor. Pulse a few times to combine. Add the butter and pulse until the mixture resembles a coarse meal, 1-2 minutes.
Add the milk, pulsing just until the dough forms a ball around the blade. The dough should be smooth and only slightly sticky.
Turn the dough onto a work surface and divide in half. Form each piece into a rectangle about 1 inch thick. Flour a work surface well and flour the dough on both sides. Roll out one rectangle of the dough to ¼ inch thick. It is prone to sticking, so be sure to rotate the dough often and re-flour as needed while you work. Use a 2 inch round cutter to cut the dough into small circles. Transfer to the prepared sheet pans, leaving about ½ inch between them. Do the same with the other portion of dough.
Prick the surface of each cracker a few times with a fork. Bake the crackers, until they are dry on the surface, 14-16 minutes. Cool completely.
Pour half of the water into a small heatproof bowl. Sprinkle the gelatin over the water and let it bloom for 5 minutes. Lightly coat a silicone spatula with nonstick spray. Fit a disposable pastry bag with a large round tip.
Combine the sugar, corn syrup, and the remaining water in a medium pot. Scrape the seeds from the vanilla bean and add them to the pot. Bring the mixture to a boil over medium-high heat – stir before it comes to a boil, but once it bubbles – stop stirring. Cook until the mixture reaches 240°F (115°C) on a thermometer.
Meanwhile, in the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on low speed until lightly frothy. Melt the gelatin in the microwave, about 30 seconds, or by setting the bowl in a shallow dish of hot water.
When the sugar reaches the right temperature, increase the mixer speed to medium-high and add the syrup in a slow, steady stream. Then, add the melted gelatin. Continue whipping until the marshmallow crème is bright white, fluffy, and holds medium peaks, 4-5 minutes.
ASSEMBLY AND FINISHING
Use the greased spatula to transfer some of the marshmallow crème to the pastry bag, filling it about halfway. Pipe a mounded spiral about 2-2 ½ inches high onto each cookie. Continue on all of the cookies, refilling the bag as needed. Let the topping set for 15 minutes.
Transfer the cookies to a cooling rack to glaze them. The chocolate glaze should be cool but still fluid. Spoon the glaze over the cookies to coat them completely. Let the cookies stand until the chocolate is firm.