Preheat oven to 350 degrees. Spray 2 8" cake pans with nonstick baking spray and set aside.
In a mixing bowl add eggs and sugar and beat on high for 3 minutes.
Add the vanilla, oil, yogurt, and espresso powder and mix to combine.
Add in the dry ingredients and gently mix to combine. Don't over mix. Add the coffee and mix.
Divide the batter between the two cake pans. Bake for 35-45 minutes or until a toothpick comes out clean. Allow to fully cool
Toasted Marshmallow Frosting
Create a double boiler by bringing a pot of water to a boil.
Place egg whites, sugar, and cream of tarter into a glass bowl and fit over the top of the pot, making sure the water never touches the bottom.
Continually whisk the mixture until it becomes frothy, 5 minutes.
Pour the mixture into a bowl and add the toasted marshmallow flavoring. Mix on high for approximately 5 minutes or until the mixture becomes thick and holds its shape.
Dark Chocolate Ganache
Melt the chocolate in the microwave. Work in 15-20 second intervals, stirring between heating, until chocolate is fully melted. Be careful not to over heat.
Stir in the cream until smooth.
S'mores Cake
Place half of the graham cracker crumbs on the first layer of cake.
Drizzle half of the chocolate ganache over the crumbs. Top with some of the marshmallow frosting.
Add the second layer of cake. Top with the remaining graham cracker crumbs and chocolate ganache.
Cover the cake in the toasted marshmallow frosting.
If desired, you can use a kitchen torch to toast the outside of the frosting.