Preheat the oven to 350°F. Place the cupcake liners into cupcake pans.
Combine the graham cracker crumbs, sugar and butter in a small mixing bowl.
Add one tablespoon of the graham cracker crust to each liner and press it flat.
Bake the crust for 6 minutes and allow them to cool completely.
Prepare the cake mix according to the directions on the box.
Fill the cupcake pan, so each one is about ¾ full.
Bake according to the directions for cupcakes on the box.
In the bowl of a stand mixer (or using an electric hand mixer), combine the butter, shortening, and marshmallow fluff and mix on medium-high speed until well combined.
Reduce the speed to low and slowly add in the powdered sugar and cocoa powder.
Mix in the milk and vanilla extract and allow the mixture to whip for 3 to 4 minutes until light and fluffy.
Place the buttercream into a piping bag with a large straight piping tip.
Pipe the buttercream onto the cupcakes.
Sprinkle the graham cracker crumbs on the cupcakes.
Using a torch or heat gun, toast the tops of the marshmallows.
Place one on each cupcake and enjoy!
Notes
You can make your own chocolate cake mix if you'd like.
These can be made mini, see above on how to do that.
Canned frosting can be used, see tips on how to make it work.
The cupcakes themselves can be frozen, do not freeze decorated.