It starts with a soft and moist cinnamon cake layer with a crunchy cinnamon layer baked right into it. The layers also have a cinnamon swirl in each cake layer. Then there is a chilled chocolate ganache and a toasted marshmallow filling. It’s then coated in a chocolate graham cracker frosting.
Preheat your oven to 325 degrees. Spray three 8-inch or four 6-inch round cake pans with non-stick cooking spray and then line with parchment paper. Spray again. Set aside.
In a medium sized bowl, whisk together flour, baking powder, salt and cinnamon. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar on medium-high speed. Cream until white and fluffy, about 5 minutes.
With the mixer on low, add the egg whites, one at a time, scraping the bowl between each addition and mixing well after each addition (at least 30 seconds).
Add the vanilla and sour cream and mix on low, just until combined. It may look a little curdled, don’t stress! Once you add the flour, it will even out.
With the mixer on low, add one third of your dry ingredients followed by half of the buttermilk, mix just until combined. Add another ⅓ of the dry ingredients mix just until combined. Add the rest of buttermilk, and then add the rest of dry ingredients. Keep mixing on low. Don’t over mix, just mix until it’s all incorporated. Use a rubber spatula to scrape the sides and the bottom of the bowl.
Divide batter evenly between the prepared pans/cooled graham cracker crust cake pans. I used a kitchen scale and got about 17 ounces in each pan. With an offset spatula, evenly spread the cake batter throughout the pan.
Before putting the cakes into the oven, make the cinnamon swirl. Mix the brown sugar, flour, and cinnamon together until combined. Add in the melted butter and mix just until combined. Immediately add it to the top of cake batter because the longer it sits out, the harder it will get as a result of the butter solidifying.
Drop small spoonfuls of the cinnamon mixture on each of the cake layers. Use a knife or toothpick to gently swirl the spoonfuls into the batter. It’s normal to have some pieces remain as chunks and some that swirl into the batter.
Bake 28-32 minutes. Check the cake by inserting a toothpick. It’s done when it comes out with just a few moist crumbs on it.
Cool 10-20 minutes before transferring the cakes out of the pans and onto a cooling rack. Cool completely before wrapping with plastic wrap and then refrigerate, if not using until the next day.
For the marshmallow filling
Place the marshmallows on a lined cookie sheet. DO NOT LINE WITH PARCHMENT PAPER. My oven doesn’t have a broil option, so I used a torch. If you don’t have a torch, directions for oven toasting are on the next step. Line the marshmallows in 5 rows, 4 in each row. With a kitchen torch, torch one side until golden brown, or darker. (I went dark to really give it that toasted flavor) Turn the marshmallows and repeat.
For oven toasting, place on the middle rack of the oven, and broil the marshmallows until golden brown on top, about 30-60 seconds. It can happen fast, so please keep an eye on them. Remove the pan from the oven and gently turn the marshmallows over and broil them again until they are golden brown on the other side.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, marshmallow fluff, and powdered sugar on low until combined. Add the vanilla and mix on medium-high speed for about 2 minutes.
Scrape down the bowl, add the toasted marshmallows, and beat on medium speed for 2 more minutes.
For the ganache
In a microwave safe bowl, pour the cream over the chocolate chips and heat for about 45-60 seconds. Stir, and if needed, heat for another 30 seconds to melt the chocolate chips completely. Let cool to room temperature before using.
For the chocolate buttercream
In a microwave safe bowl, heat the chocolate for 30 seconds, stir, heat for 30 more seconds, and set aside. The chocolate will not be melted all the way, but this will help it melt quicker when you add the cream.
In another microwave proof bowl, heat the cream until nearly boiling. Make sure it doesn’t boil over. Pour the hot cream over the slightly warm chocolate chips. Let it sit for 2 minutes and then stir. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter for about 2 minutes on medium-high speed.
Add the chocolate/cream mixture. Scrape down the sides and bottom of the bowl with a rubber spatula and beat for 1 more minute.
Add the powdered sugar, vanilla, graham cracker crumbs, cinnamon, and salt. Mix on low until combined, then turn the mixer to medium high, and beat for 3 minutes.
With a wooden spoon or a rubber spatula, beat by hand to mix out any air pockets.
Assembly
Level the cakes with a cake leveler, if needed.
Place the first cake layer top side up on a cake board with a dollop of frosting in the middle of the cake board to act as glue. Pipe a rim of chocolate around the edge of the cake.
Spread half of the chocolate ganache on the cake layer and then freeze for 5 to 10 minutes to set the ganache a little.
After the ganache has set a tad, spread half of the marshmallow filling on top of the set ganache and within the piped chocolate rim.
Repeat with the second layer of cake.
Place your final cake layer with the top side down on top of the second layer of filling.
Apply a thin layer of the chocolate buttercream around the entire cake and freeze the cake for 10 to 15 minutes.
Once the crumb coat is set, finish frosting and decorating the cake with the remaining chocolate buttercream. Serve at room temperature.