Preheat oven to 350˚F.
Line the bottom of 3 (6 inch) cake pans with parchment paper and lightly grease and flour.
Pour graham cracker crumbs, flour, baking powder, baking soda, and salt into a mixing bowl and whisk together. Set aside.
Place butter and both sugars in a mixing bowl and beat together until light and fluffy.
Add eggs, one at a time, scraping down after each addition, then stir in vanilla.
Alternate adding the dry ingredients and buttermilk into the wet mixture and beat together until fully incorporated and the batter is smooth.
Evenly divide the batter between the prepared cake pans and bake for about 35 minutes or until a toothpick comes out clean when inserted into the center of the cakes.
Remove cake pans from the oven and place onto a cooling rack for about 30 minutes.
Release each cake round from the cake pans and refrigerate cakes for 2 to 4 hours.
For ganache: Pour milk into a saucepan and scaled over medium heat. Once milk is hot, remove from heat and add chocolate. Allow the mixture to sit for 5 to 7 minutes. Stir the melted chocolate and milk together until completely combined and smooth. Refrigerate for about 2 hours, or until the ganache has set.
Make 1 recipe of marshmallow fluff
To assemble: Slice each cake in half, horizontally. Set aside.
Using a hand mixer, whip ganache until light, fluffy and smooth.
Spread a layer of whipped ganache between each layer of cake and neatly stack them atop one another. Frost the sides and top with a thin layer of ganache.
Spread a thick layer of homemade marshmallow fluff around the entire cake (the more swoops, the better the cake will look when torched).
Carefully torch the marshmallow fluff until entire cake is toasted. Slice and serve.