Instructions

for the cookies

Adjust oven rack to middle position and heat oven to 350 degrees. Line 2 rimmed baking sheets with parch ment paper. Whisk all-purpose flour, graham flour, sugar, baking powder, baking soda, salt, and cinnamon together in bowl of stand mixer. Add melted butter, water, molasses, and vanilla. Using paddle attachment, mix until dough comes together, about 20 seconds.
Transfer dough to counter and divide into 2 equal pieces. Working with 1 piece of dough at a time (keep remaining piece covered with plastic wrap), roll into 12-inch circle, ⅛ inch thick, between 2 large sheets of parchment. Remove top piece of parchment. Using 3-inch round cookie cutter, cut dough into 8 rounds; carefully transfer rounds to prepared sheets, spacing ½ inch apart. Gently reroll scraps into 8-inch circle, ⅛ inch thick, then cut into 4 rounds and transfer to sheets.
Bake cookies, 1 sheet at a time, until edges are set, about 10 minutes, rotating sheet halfway through baking. Transfer sheet to wire rack and let cookies cool completely. (Cookies can be stored in airtight container for up to 1 day.)

for the filling

Whisk 3 tablespoons water and gelatin together in clean, dry bowl of stand mixer fitted with whisk attachment. Let sit until very firm, about 5 minutes.
Meanwhile, combine corn syrup and remaining 3 tablespoons water in small saucepan. Pour sugar and salt into center of saucepan (do not let sugar hit saucepan sides). Bring to boil over medium-high heat and cook, gently swirling saucepan, until sugar has dissolved completely and mixture registers 240 degrees, 4 to 6 minutes.
Turn mixer speed to low and carefully pour hot syrup into gelatin mixture, avoiding whisk and sides of bowl. Gradually increase speed to high and whip until mixture is very thick and stiff and coats whisk, about 7 minutes, scraping down bowl as needed. Add vanilla and mix until incorporated, about 15 seconds.
To assemble, place 12 cookies upside down on counter. Working with 1 cookie at a time, place 2 tablespoons marshmallow filling in center of cookie and spread evenly with back of spoon. Place second cookie on top of filling, right side up, and gently press and twist until filling is even with edges of cookies. Let sit for 15 minutes until filling is set.
Line baking sheet with clean sheet of parchment. Microwave chopped chocolate in medium bowl at 50 percent power, stirring often, until about two-thirds melted, 2 to 4 minutes. (Melted chocolate should not be much warmer than body temperature; check by holding bowl in palm of your hand.) Add grated chocolate and coconut oil and stir until smooth, returning to microwave for no more than 5 seconds at a time to finish melting if necessary.
Rotate filling-exposed side of 1 sandwich cookie in chocolate until filling and cookie edges are fully covered. Place sandwich cookie in chocolate and, using 2 forks, gently flip to fully coat all sides. Lift cookie out of chocolate with fork. Using offset spatula, spread chocolate on top of cookie into thin, even layer, allowing excess to run off sides. Tap fork against edge of bowl, then wipe underside of fork on edge of bowl to remove excess chocolate from bottom of cookie. Use second fork to slide sandwich cookie onto prepared sheet. Repeat with remaining sandwich cookies, returning chocolate to microwave for no more than 5 seconds at a time if it becomes too firm.
Refrigerate sandwich cookies until chocolate is set, about 20 minutes, before serving. (Sandwich cookies can be stored at room temperature for up to 2 days.)