A graham cracker cake, lots of chocolate and amazing home made marshmallow fluff combine to make a sure to please treat.
Set oven to 350F. Butter and flour 3 6" cake pans (I recommend using cake stripes as well.
Whisk all the dry ingredients together in a medium bowl. In a separate bowl, mix the buttermilk, vanilla and sour cream.
Cream the butter in a stand mixer and add sugars. Mix until light and fluffy.
Add the eggs and white in one at a time mixing until incorporated.
Add the flour mixture and the buttermilk mixture in alternating batches. Starting and ending with the flour mixture. Mix until just combined, give the bowl a final scrape with a spatula to get any unmixed parts on the sides and bottom.
Pour batter into your pans and bake for about 30 minutes or until a knife comes out clean from the center.
Beat the butter until light and fluffy, add in confectioner's sugar in several batches and beat until incorporated. Drizzle in melted chocolate and mix until well combined. If buttercream is too thick at this point you can add some cream or milk, a tablespoon at a time until desired consistency is reached.
Add 2/3 cup sugar and corn syrup to a small sauce pot and heat on medium high. Track the temperature with a candy thermometer you will want to pour into the egg whites when it is 240F.
In a stand mixer start beating the egg whites starting on low but gradually gradually increasing to medium-high speed. Add in 1/3 cup of sugar while the egg whites are stiffening. Once you are at the soft peak stage slowly drizzle in the 240F sugar syrup into the mixer.
Allow the mixer to run for about 10 minutes to allow the fluff to cool.
You can use immediately, if the fluff looses it's texture give it a good wisk or run the mixer for a few seconds to bring it back.
Mix the melted butter and graham cracker crumbs together well.
Flatten out to about 1/4" onto a baking sheet lined with parchment paper.
Bake for about 10 minutes at 350F or until you see a slight browning.
Allow to cool and then crumble the mixture roughly allowing some larger pieces to remain.
Pipe a ring of the chocolate buttercream on each layer and fill with marshmallow fluff. Sprinkle with graham cracker crumble and drizzle with melted chocolate.
Apply a thin crumb coat and allow to set in the refrigerator for about 20 minutes.
Coat with chocolate buttercream, smooth edges with an offset spatula.
press cracker crumbs onto the bottom third of the cake and then pipe the fluff onto the top.
Flame the fluff with a torch and cake is ready to serve.