Preheat Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
Make the Crust: In a medium bowl, combine 1 cup graham cracker crumbs, 1/4 cup sugar, and 1/4 cup melted unsalted butter. Mix until the ingredients are well combined. Press the mixture into the bottom of the cupcake liners firmly. Bake for 5 minutes to set the crust.
Prepare the Cupcake Batter: In a separate bowl, whisk together the dry ingredients: 1 cup all-purpose flour, 1 cup granulated sugar, 1/2 cup cocoa powder, 1 tsp baking powder, 1/2 tsp baking soda, and 1/4 tsp salt. In another bowl, mix together the wet ingredients: 1/2 cup milk, 1/2 cup oil, 1 large egg, and 1 tsp vanilla extract. Gradually blend the wet ingredients into the dry mixture until smooth, then stir in 1/2 cup hot water carefully.
Bake the Cupcakes: Pour the batter evenly over the baked crusts in the muffin tin. Bake for 18-20 minutes, or until a toothpick inserted comes out clean. Allow the cupcakes to cool completely in the tin before removing.
Make the Frosting: In a large bowl, beat 1 cup softened butter until creamy. Add 2 cups marshmallow fluff and 3 cups powdered sugar gradually, mixing until fluffy. If the frosting is too thick, add 1-2 tbsp milk to achieve the desired consistency.
Decorate the Cupcakes: Once the cupcakes are completely cool, pipe the fluffy marshmallow frosting onto each cupcake generously. Top with mini marshmallows, graham cracker pieces, and drizzle with melted chocolate for added flair. Optionally, toast the mini marshmallows slightly using a kitchen torch for an authentic s’mores experience.