Preheat the oven to 350 degrees F. Add cupcake liners to the cupcake pan and set aside.

In a medium sized bowl, combine the dry ingredients (flour, sugar, cocoa powder, baking soda and salt).

In a larger bowl, combine the wet ingredients (oil, eggs, milk and vanilla).

Add the dry ingredients into the wet and whisk until just combined.

Fill cupcakes ¾ the way full and bake for 20 minutes or until a toothpick inserted into the middle comes out clean. Transfer the cupcakes to a cooling rack and allow to fully cool before frosting.

Meanwhile, make the frosting by adding the butter to a large mixing bowl. With an electric or stand mixer, mix on medium speed for 1 minute.

Add in the powdered sugar 1 cup at a time.

Pause to scrape the sides of the bowl. Add the hot chocolate packet, cocoa powder and heavy cream.

Mix again until a smooth, fluffy frosting has formed. Transfer to a piping bag.

Put the marshmallow fluff in another piping bag.

Using a knife, cut a half inch hole in the top of each cupcake stopping just before the bottom.

Fill each cupcake with the fluff and top with the chocolate frosting.

Add a few marshmallows on top of each cupcake.