Prepare the Cupcakes:
Preheat the oven to 350°F (175°C). Line a cupcake pan with 6 liners.
In a mixing bowl, cream together butter and sugar until light and fluffy. Beat in the egg and vanilla.
In a separate bowl, whisk together cinnamon, salt, baking powder, flour, and graham cracker crumbs.
Gradually add the dry ingredients to the wet, alternating with milk. Mix until smooth.
Divide batter evenly among cupcake liners. Bake for 18–20 minutes or until a toothpick comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Make the Marshmallow Filling:
In a heatproof bowl, combine egg white, sugar, and cream of tartar.
Place over a pot of simmering water and whisk constantly until sugar dissolves and mixture is warm (about 3–4 minutes).
Remove from heat and beat with a mixer until stiff, glossy peaks form (5–7 minutes). Beat in vanilla.

Fill the Cupcakes:
Cut a small hole from the center of each cooled cupcake. Fill with marshmallow fluff using a spoon or piping bag.

Make the Frosting:
Beat butter until creamy. Sift in powdered sugar and cocoa powder. Add vanilla and milk, and beat until smooth and fluffy.

Frost the Cupcakes:
Pipe or spread chocolate frosting on top of each cupcake. Enjoy!