Instructions

1. Preheat your oven to 350 degrees F.
2. Butter two 9-inch round cake pans, and line them with circles of parchment paper, then butter or coat with nonstick cooking spray.
3. In a medium bowl, whisk together flour, graham-cracker crumbs, baking powder, baking soda, salt, and cinnamon. Set aside.
4. In a large mixing bowl, cream butter and sugars together until light and fluffy. Add eggs one at a time, scraping the bowl down after each addition.
5. Add a third of the dry ingredients, then half the buttermilk, a third of the dry ingredients, the remaining buttermilk, and then the remaining dry ingredients, mixing between additions until combined. Scrape down bowl, and mix again briefly if needed.
6. Divide batter between prepared cake pans, smoothing tops.
7. Bake until a toothpick inserted into the center comes out clean, about 30-35 minutes. Cool in pan on rack, then run a knife between the cake edges and pans before inverting each layer on a rack, discarding the parchment paper, and flipping back upright onto a rack. Let cool completely, a process you can speed up in the fridge.
8. Make the filling: Place the chocolate in a heatproof bowl. Combine the heavy cream and salt in a small saucepan, and bring to a simmer.
9. Pour over the chocolate, and let sit for 1 minute, then whisk until smooth. Set bowl over another bowl filled with ice water, and stir it until it firms up to a spreadable consistency. You can also let it cool down in the fridge, stirring it from time to time so it thickens evenly.
10. Prepare the cake: Arrange a single cake layer on a serving platter or cake stand. For a neat-looking cake, use a long serrated knife to level the top gently, taking off only the domed part (which shouldn't be much); place scraps in a bowl where husbands and other housemates can enjoy the preview.
11. Spread chocolate thickly over bottom layer. Place the top layer over bottom layer. Once again, for a neater appearance, you can level the top off the cake in the same manner, but I won't tell anyone if you don't share the scraps. Baking is exhausting work, after all.
12. Make the frosting: Place egg whites, granulated sugar, and cream of tartar in the heatproof bowl of an electric mixer. Set over a saucepan with simmering water. Whisk constantly until sugar is dissolved and whites are warm to the touch, about 3 minutes.
13. Transfer the bowl to an electric mixer fitted with the whisk attachment, and beat, starting at low speed, gradually increasing to high, until stiff, glossy peaks form, 4-7 minutes. Add vanilla, and mix until combined. You'll want to use this immediately.
14. Frost the cake: Spread a thin layer of the frosting over the top and sides, covering all of the crumbs (and binding them to the cake). Transfer the cake to the fridge for 5 or 10 minutes, to let it set a bit, then generously coat the top and sides with additional frosting.
15. Pipe the remaining frosting (if you have it) in marshmallow-like dollops decoratively over the top. (I didn't do this part, so I have no wisdom to share.)
16. With a kitchen torch on a low setting, lightly brown the top, creating a toasted-marshmallow effect.