Equipment:Pastry brush, 15- by 10-inch jelly roll pan, fine-mesh sieve, stand mixer fitted with the whisk attachment and paddle, candy thermometer, small offset spatula, 3-inch round cookie cutter, 2 1/2- to 2 3/4-inch round cookie cutter, parchment paper, rolling pin, 2 large rimmed baking sheets
Make the marshmallows:
Brush the bottom and sides of a 15- by 10-inch jelly roll pan with vegetable oil. Using a fine-mesh sieve, dust the bottom and sides of the pan with 1/4 cup of the sifted confectioners’ sugar, leaving any excess in the pan.
Place 6 tablespoons of the cold water in the bowl of a stand mixer fitted with the whisk attachment. Sprinkle the gelatin into the bowl and whisk briefly to make sure all the gelatin is in contact with water. Let soften while you make the sugar syrup.
In a heavy, small saucepan, whisk together the granulated sugar, corn syrup, salt, and the remaining 6 tablespoons cold water. Place over moderate heat and bring to a full boil (the mixture will become clear), stirring until the sugar is dissolved. Put a candy thermometer into the boiling sugar syrup and continue boiling, without stirring, for 5 minutes, then increase the heat to moderately high and continue boiling, without stirring, until the thermometer registers 240°F (soft-ball stage), about 5 more minutes. Remove the saucepan from the heat and let stand until the bubbles dissipate slightly.
With the mixer on low, pour the sugar syrup into the softened gelatin in a thin stream down the side of the bowl. Gradually increase the mixer speed to high and beat until the marshmallow forms a very thick ribbon when the whisk is lifted (the marshmallow will still be slightly warm), about 5 minutes.
Scrape the marshmallow into the prepared pan (it will be very sticky) and use wet fingertips to spread it evenly; smooth the top with a wet offset spatula. Dust the remaining 1/4 cup confectioners’ sugar over the top of the marshmallows, then cover the pan with plastic wrap, being careful not to let the plastic wrap touch the marshmallow as they will stick together. Set the marshmallow aside to firm up, at least 4 hours or overnight.
Once the marshmallows are firm, use a 3-inch round cookie cutter to cut out 12 marshmallow circles—you will need to cut the marshmallows very close together so there are very few scraps. Dust the marshmallows with additional confectioners’ sugar to prevent sticking DO AHEAD: Marshmallows can be stored, layered between sheets of wax or parchment paper, in an airtight container in a dry place at cool room temperature, for 1 week.
Make the graham crackers:
Position a rack in the upper third of the oven and a second rack in the lower third then preheat to 350°F.
In a medium bowl, whisk together the all-purpose flour, pastry flour, wheat germ, salt, cinnamon, and baking soda.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed until light and fluffy, about 5 minutes. Add the cane syrup and honey and beat until well combined, about 1 minute. Scrape down the sides and bottom of the mixer bowl then reduce the mixer speed to medium-low, add the flour mixture, and blend just until no streaks of flour remain, 1 to 2 minutes—the mixture will be a little crumbly.
Divide the dough into 2 equal portions. Place 1 half on a large sheet of parchment paper then cover with a second large piece of parchment paper. Using a rolling pin, roll the dough, between the sheets of parchment paper, to a 1/8-inch thickness. Remove the top layer of parchment and use a 2 1/2 to 2 3/4-inch round cookie cutter to press as many circles into the dough as possible. Use a small offset spatula to transfer the graham crackers to a large rimmed baking sheet, leaving about 1 inch between them then re-roll and cut any scraps of dough to make more circles. Repeat this process with the remaining portion of dough.
Bake the graham crackers, switching the baking pans between the upper and lower racks and rotating the pans about halfway through baking, until the graham crackers are firm around the edges and golden, 12 to 14 minutes. Transfer the graham crackers to a wire rack to let cool completely. DO AHEAD: Graham crackers can be baked ahead and kept, stored in an airtight container at room temperature, up to 1 week.
Melt the chocolate and assemble the moonpies:
Sandwich 2 graham crackers around 1 marshmallow then repeat with the remaining graham crackers and marshmallows until you have 12 moon pie “sandwiches.” (There may be a few leftover graham crackers.)
Coat a wire rack with nonstick vegetable oil spray and set it on top of a parchment paper– lined large rimmed baking sheet.
Place about 2/3 of the chocolate in a dry metal bowl set over a pan of barely simmering water and stir until melted and warm, 2 to 3 minutes. Add the remaining chocolate to the bowl and remove the bowl from the top of the pot. Let cool 5 minutes then stir until smooth. Stir in the coconut oil until incorporated thoroughly.
Hold 1 moonpie “sandwich” firmly in 1 hand and roll the sides through the melted chocolate, making sure the sides are completely coated so you don’t see any marshmallow peeking through. Hold the moonpie over the bowl of chocolate and use a small spoon to pour and swirl chocolate over the top; invert onto the rack and coat the other side in chocolate. Repeat with the remaining graham cracker–marshmallow “sandwiches.” Transfer the chocolate-dipped moonpies to a cool place to let the chocolate coating harden for 1 to 2 hours. DO AHEAD: Moonpies can be made ahead and kept, layered between sheets of parchment paper in an airtight container at room temperature, up to 5 days.