Preheat oven to 350°F and place 12 cupcake liners in a cupcake tin. Put graham crackers in a ziploc bag and crush with a rolling pin. In a medium bowl, add graham cracker crumbs, butter, and sugar and mix well.
Place a heaping tablespoon of the crust mixture in the bottom of each cupcake liner and press down. Bake crusts for 5 min. Remove and set aside to cool while you make the cupcakes.
Start making the cupcakes. In a stand mixer with paddle attachment, beat together the egg, buttermilk, vegetable oil and vanilla extract until smooth.
In a medium bowl, sift together the flour, sugar, cocoa powder, baking soda, baking powder and salt.
Add the flour mixture and mix on low speed until there are no longer any clumps. Add the coffee and mix until combined.
Pour the batter ⅔ full among the muffin tins and bake for 12-15 minutes or until a toothpick inserted into the center of a cupcake comes out clean. When cupcakes are done remove immediately from tins and leave on a cooling rack to cool completely before adding the frosting.
Marshmallow Frosting
Combine egg whites, sugar, and cream of tartar in a metal heat proof bowl. Place bowl over a saucepan with boiling water. Whisk constantly until sugar is melted and mixture is warm to touch or between 120°F and 140°F on a candy thermometer.
Remove from heat and pour into the bowl of an electric mixer. Using the whisk attachment, beat on a low speed gradually increasing to high speed until stiff, glossy peaks form, about 7-9 minutes. Add vanilla extract with 30 seconds left.
Spoon frosting into piping bag and pipe onto the cupcakes. Torch the frosting to add a roasted marshmallow look if desired and top with graham cracker crumbs.
Notes
Do not skip the buttermilk as it helps create the moistness you expect from chocolate cupcakes.
All refrigerated items should be at room temperature, which helps the batter mix easily and evenly. Also super important for the frosting.
When adding the batter to the muffin tin, don't fill more than ⅔ of the way as they do rise.
Separate your eggs into a smaller separate bowl so that if one of the yolks breaks for your frosting, you haven’t ruined the batch.
Pipe the frosting immediately as it sets quickly and becomes difficult to work with.
Allow the cupcakes to completely cool before adding the frosting, otherwise it will melt.