Preheat oven to 350 degrees F. Lightly grease and flour 3 8-inch round cake pans lined with parchment paper (you can also use 2 9-inch but will want to bake longer).

Sift the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl and whisk until combined.

In the bowl of an electric mixer fitted with the whisk attachment, mix the buttermilk, oil, eggs, and vanilla.

With the mixer on low speed, slowly add the dry ingredients. With mixer still on low, add the coffee and stir just to combine. Pour the batter into the prepared pans and bake for 18-20 minutes, or until a cake tester or toothpick comes out mostly clean.

Cool in the pans for 30 minutes, then turn them out onto a cooling rack to cool completely.

Place the marshmallows on a baking sheet lined with aluminum foil and sprayed with nonstick cooking spray. Place on the lowest rack of oven, and broil marshmallows until nice and brown on top (about 1 to 2 minutes- keeping an eye on them the entire time so they don’t burn). Remove pan from oven and gently turn the marshmallows over, and broil until the other side is golden brown.

Beat the butter and powdered sugar on low speed until blended together, about 1 minute. Add the vanilla extract and increase the speed to medium-high and beat for 3 minutes. Add the Marshmallow Fluff and toasted marshmallows, and mix on the lowest speed for 1 to 2 minutes, scraping the sides of the bowl as necessary.

In a small bowl, combine the graham cracker crumbs, sugar, and melted butter and stir until well combined and crumbly. Spread mixture onto a cookie sheet lined with parchment paper. Bake at 350° F for about 5 minutes, then remove and set aside to cool.

With an electric mixer fitted with your paddle attachment, beat the butter on medium speed for about 2 minutes.

Add the peanut butter and beat until well combined (about 1 minute).

Add half of the powdered sugar and beat on low speed until combined. Add the remaining powdered sugar and beat until combined.

Add 1 tablespoon of heavy cream and beat on low speed for 30 seconds. Continue adding a tablespoon at a time until you reach your desired consistency. Beat for an additional 3-5 minutes on low speed.

Heat the heavy cream in a microwave-safe bowl in the microwave until almost boiling, about 45 seconds. Add the chocolate chips and let sit for about 2 minutes. Slowly stir and well combined. Let ganache cool to room temperature before using (I place mine in the refrigerator for about 15 minutes to cool).

In a large, clean metal bowl, combine the egg whites and sugar (make sure the bowl is completely clean there is even a trace of fat in the bowl, the eggs won’t reach their proper volume).

Set the bowl over a saucepan with 2 inches of simmering water (make sure the water does not touch the metal bowl).

Heat the egg whites and sugar whisking constantly, until the sugar melts and there is no visible grains in the meringue (rub a little bit of the meringue between your fingers to make sure all the grains have melted).

Remove from the heat and beat using an electric mixer fitted with the whisk attachment on low speed for 5 minutes. Increase the speed to high and beat 5 minutes longer or until the meringue is stiff and shiny.

Place one cake layer upside down on a cake plate or stand and spread 1-2 cups of toasted marshmallow filling on the cake. Add a layer (about ½ - ¾ cup) of graham cracker crumbs on top. Repeat with second layer. Add third cake layer and frost a thin layer of peanut butter buttercream on the sides and top (crumb coat). I usually put it in the fridge or freezer at this point for 5-10 minutes and then add additional frosting to the top and sides. Add remaining graham cracker crumbs to the bottom of the cake.

Add half of the chocolate ganache to a drip bottle, and drip along the top edges of the cake. Add the remaining ganache on top of the cake and slowly smooth out with a knife or offset spatula, being careful not to let it run over the edges. Place cake in fridge for 30 minutes to an hour for the ganache to set.

Meanwhile, make the marshmallow meringue. Remove cake from fridge and using a knife or offset spatula, add marshmallow meringue to top of cake.

Torch with a kitchen torch, if desired.