Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them with butter and lining the bottoms with parchment paper. Sprinkle a thin layer of graham cracker crumbs in the pans.

In a medium bowl, mix together graham cracker crumbs, melted butter, and sugar until well combined. Press this mixture evenly into the bottom of each prepared cake pan. Bake the crusts in the preheated oven for 10–12 minutes or until lightly golden brown.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, Dutch-process cocoa powder, baking soda, baking powder, and salt until well blended.

In a separate bowl, mix the large eggs, buttermilk, hot brewed coffee, neutral oil, and pure vanilla extract until smooth. Gradually pour the wet ingredients into the dry mixture, combining until just mixed.

Evenly divide the batter between the cooled graham cracker crusts. Bake in the oven for 25–30 minutes, or until a toothpick inserted in the center comes out with moist crumbs. Let the cakes cool in the pans for 10 minutes before transferring them to wire racks to cool completely.

Prepare the dark chocolate ganache by heating the heavy cream in a saucepan until it simmers. Pour it over the chopped dark chocolate in a heatproof bowl and stir until smooth and glossy.

In a large mixing bowl, whip the egg whites and granulated sugar together until stiff peaks form. Gradually add in the softened butter and marshmallow fluff, mixing until you achieve a light and airy frosting consistency.

To assemble the cake, place one layer on a serving plate. Spread a generous layer of the chocolate ganache over the first cake layer. Carefully place the second cake layer on top, then apply a thin crumb coat of the marshmallow frosting around the sides and top of the cake.

Cover the cake with a thick layer of marshmallow frosting. Toast the frosting peaks if desired, and garnish with mini marshmallows and crushed graham crackers.