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.
¾ Cup Cocoa Powder, 2 Cups All Purpose Flour, 2 Cups Granulated Sugar, 2 Tablespoons Corn Starch, 2 teaspoons Baking Powder, ½ teaspoon Baking Soda
Add oil and eggs. Mix until combined.
¾ Cup Vegetable or Canola Oil, 4 Large Eggs
Slowly pour brewed coffee into bowl while continuing to mix, scraping the bowl occasionally. The batter should be smooth.
1 ¼ Cup Brewed Coffee
Divide batter between the two prepared cake pans.
Bake for 35 - 40 minutes. Cake will be well risen and a toothpick inserting in the center will come 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
6 Tablespoons Unsalted Butter
Line two 8" round pans with plastic wrap, making sure it covers the bottom and sides. This will help you lift the graham cracker discs out of the pans easily.
Combine graham cracker crumbs and granulated sugar in a bowl. Add melted butter to the bowl and mix well.
2 Cups Crushed Graham Crackers, ⅓ Cup Granulated Sugar
Lightly press the graham cracker mixture into two 8" pans, dividing it evenly between the two pans. Place pans in the freezer to set.
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.
8 Large Egg Whites, 2 Cups Granulated Sugar, ½ teaspoon Sea Salt, 1 Cup Light Corn Syrup
Place the bowl over a pot of simmering water, making sure the bottom of the bowl doesn’t touch the water and the water does not boil. Whisk occasionally, about every 2–3 minutes.
Continue to heat until the mixture reaches 160℉ (71℃)
Place the bowl on the stand mixer and, using the whisk attachment, whip the mixture until the icing has cooled completely. It should become fluffy, white, and hold stiff peaks.
Cake Assembly
Carefully slice the domed top off each chocolate cake to level them. Then, slice one of the cakes horizontally into two even layers.
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 of the graham cracker discs on top of the chocolate cake layer with the marshmallow icing, pressing gently so it sticks to the filling. Then spread a thin layer of marshmallow icing evenly over the top of the graham cracker.
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 graham cracker disc on top of the filling. 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.
Use the back of a spoon or an offset spatula to gently swirl and lift the marshmallow frosting, creating decorative peaks and texture on the surface.
Optional: Using a kitchen torch, gently toast the peaks of the marshmallow frosting until golden brown. Add any decorative touches you like, such as graham cracker pieces, chocolate chips, or a drizzle of melted chocolate.