Preheat the oven to 350 degrees F. Spray three 8-inch round baking pans with nonstick baking spray - make sure it’s the kind that has the flour in the spray!
In a bowl, whisk together the flour, sugar, cocoa, baking soda, powder and salt.
In the bowl of your electric mixer fitted with a paddle attachment, beat the buttermilk, oil and eggs on medium speed until combined. Beat in the vanilla extract. With the mixer still on medium speed, beat in the dry ingredients until they are just combined, scraping the bottom and sides of the bowl if needed. Beat in the coffee until combined.
Divide and pour the batter into the prepared cake pans. Bake the cakes for 30 to 35 minutes, or until a tester inserted in the center comes out clean. Let the cake cool for about 30 minutes in the pan, then carefully invert onto parchment paper to let them cool completely.
I actually like to do this part ahead of time. Once cool, I wrap the cake layers in plastic wrap and stick them in the freezer, if only for 30 minutes. This helps the frosting go on nicely!
When you’re ready to frost, add a dollop of frosting on top of two cakes and layer the cakes together. Add the remaining frosting and cover the cake.
Pipe the whipped marshmallow on top of the cake. Sprinkle with cocoa powder. Slice and serve when you’re ready!
We love to keep this cake in the fridge (Eddie loves cold cake!) and I would recommend that since it has the cream cheese frosting. Bring it out 30 to 60 minutes before serving so it can come to room temperature.