Prepare two 8" cake pans by lining the bottom with parchment paper or greasing the pans.
Combine flour, cocoa powder, sugar, cornstarch, baking powder and baking soda in the bowl of a stand mixer. If mixing by hand or with a hand mixer, combine ingredients in a large mixing bowl.
Add oil and eggs. Mix until combined.
Slowly pour brewed coffee into bowl while continuing to mix, scraping the bowl occasionally. The batter should be smooth.
Divide batter between the two prepared cake pans.
Bake for 10 minutes at 275°
Increase oven temperature to 350° and bake an additional 25 minutes, or until cake is fully risen and a toothpick inserted in the center of the cake comes out clean.
Place cakes on a rack and allow to cool completely before unmolding. Unmold by running an offset spatula or knife around the inside of the cake pan and flip pan over onto a platter.
Graham Cracker Crust Layers
Melt butter and allow to cool slightly
Line two 8" round pans with plastic wrap
Combine graham cracker crumbs and granulated sugar in a bowl. Add melted butter to the bowl and mix well.
Lightly press ½ of the graham cracker mixture into each pan. Place pans in freezer.
Marshmallow Filling and Frosting
Place egg whites, sea salt, sugar and corn syrup in a bowl of a stand mixer. Whisk by hand to combine.
Place bowl over a pot of simmering water. The bottom of the bowl should not touch the water. Whisk occasionally – every 2 – 3 minutes.
Continue to heat until the mixture reaches 160° F
Place the bowl on the mixer and using the whip attachment, whip until the icing has cooled. The icing will be fluffy, white and hold stiff peaks.
Cake Assembly
Slice the domed top off of each chocolate cake. Slice one of the cakes into two slices.
Place one of the smaller slices of chocolate cake onto a serving platter. Spread a thin layer of the marshmallow frosting on top of the chocolate cake.
Remove graham cracker pans from the freezer. Unmold by pulling upward on the plastic wrap.
Place one layer of the graham cracker crumbs on top of the chocolate cake layer with the marshmallow icing. Spread marshmallow icing on top of the graham cracker layer.
Place the large layer of chocolate cake on top of the marshmallow topping and press down on the cake lightly. Spread a thin layer of the marshmallow frosting on top of the chocolate cake.
Place the second layer of the graham cracker crumbs on top of the cake. Spread marshmallow frosting on top of the graham cracker layer.
Place the last layer of chocolate cake on the top. Spread a thick layer of marshmallow frosting on the top and sides of the cake.
Using the backside of a spoon or offset spatula, create peaks in the marshmallow frosting.
Optional: Using a kitchen torch, lightly brown the peaks of the marshmallow frosting.