Preheat oven to 300°F. Grease three 9"-round baking pans. Press parchment paper into bottoms of pans, then grease top-side of parchment paper.
For the Cake: Chop up the dark chocolate bar and place pieces in a ceramic bowl. Pour hot coffee over top of the chocolate and stir for a few seconds until smooth. The chocolate should melt very quickly. Set chocolate/coffee mixture aside.
In a bowl, combine sugar, flour, cocoa powder, baking soda, baking powder, and salt.
In a separate bowl, lightly beat eggs, then add canola oil, coconut oil, buttermilk, and vanilla extract. Pour wet ingredients into dry and stir until just combined. Stir in chocolate chips.
Pour cake batter evenly into three pans. I found that the chocolate chips tended to stick towards the bottom of the bowl and not flow evenly with the batter into the pans, so use spatula to ensure that chips are evenly distributed throughout the layers.
Bake until a toothpick inserted in the center is clean. This took about 45-50 minutes for me, though the original recipe calls for less time, so I would suggest starting to check earlier.
Let layers cool in pans for a few minutes, then turn out onto a wire rack to cool completely.
For the Filling: Line a baking pan with aluminum foil, then spray foil with cooking spray. Place marshmallows on foil, then place pan in oven with the "broil" setting until the tops of the marshmallows start to expand and the tops become golden-brown. Remove pan from oven, flip marshmallows over, then broil until tops become golden-brown, as well. This step is very quick - continually watch the marshmallows because they can go from perfect doneness to burnt in a matter of seconds.
Beat powdered sugar and butter on low speed until mixture is smooth and powdered sugar is fully worked into the butter. Increase speed to medium, then add cocoa powder, almond extract, marshmallows, and marshmallow cream. Beat for a few minutes until all ingredients are well integrated and the filling as a creamy, spreadable consistency.
Once cake layers have cooled completely, place one layer onto serving dish, spread half of the marshmallow filling over top, place another cake layer, spread remaining marshmallow filling, then top with the third cake layer.
Frost using your favorite chocolate frosting recipe (I used Pixelated Crumb's chocolate ganache, link below) and decorate as you please (sprinkles, cookie crumbs, etc.)