For the Graham Cracker Cake: Preheat the oven to 375°. Line the bottom of two 9-inch round cake pans with parchment or wax paper. Spray each pan with cooking spray. In a medium bowl, combine the graham cracker crumbs, baking powder and salt; stir together and set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on medium-high speed until soft peaks form. Transfer to a separate bowl and set aside. Replace the mixer bowl and fit with the paddle attachment. Cream together the butter and sugar and beat on medium speed until light and fluffy, about 2 minutes. Mix in the egg yolks until well combined. Stir in the vanilla extract.
Add in the dry ingredients alternately with the milk on low speed, beginning and ending with the dry ingredients and mixing just until incorporated. Using a rubber spatula, fold in about a third of the egg whites to lighten the batter. Gently fold in the remaining egg whites until completely incorporated. Batter will look a little strange! Don't be worried.
Divide the batter evenly between the prepared pans. Bake the cakes for about 18-20 minutes or until a toothpick inserted in the center comes out clean. Allow the cakes to cool in the pans for about 5-10 minutes, then invert onto a wire rack, remove the parchment paper, and cool.
Once the cake has cooled completely, transfer one of the cake layers to the serving platter. Carefully spread a layer of marshmallow fluff over the cake, not quite reaching the edges. Top with the remaining cake layer and refrigerate for about 1 hour or until firm.
Once cake has cooled prepare the Milk Chocolate Frosting. Combine the chocolate, cream, butter and corn syrup in a microwave safe bowl. Heat in 30 second intervals or until the chocolate has melted. Whisk the ingredients together until completely smooth. It will be thin. Pour frosting over the top of the chilled cake, allowing it to run down the sides in some places.
Let frosting set slightly so that your decorations don't just run down the side. Once it has set slightly, garnish with mini marshmallows, chocolate chips, and graham cracker crumbs. Return to the refrigerator to chill until set.
Cake will set up quickly, and should be stored in the refrigerator if not being served shortly after being assembled.
Notes
Note: If you grind your own grahams in the food processor, you’ll need about 20-22 graham crackers.Source: Annie's Eats ; original recipe Baking Bites