Heat your oven to 325℉.
To a bowl or a stand mixer, add in all dry ingredients for the cupcake and mix until combined.
Add in your egg, milk, water, and oil one at a time until fully combined.
Once your batter is smooth, fill your cupcake pan about 3/4 of the way and bake for 17-20 minutes, or until fully cooked. Check doneness by poking the middle with a toothpick. Once cooked, set aside to cool.
To a bowl, combine the confectioner's sugar, heavy cream, and vanilla and whisk until smooth. Add to a piping back or Ziplock bag with the corner cut and set aside.
Add your marshmallow fluff to a piping bag or Ziplock bag with the corner cut and set aside.
Fill the cupcakes with fluff and smooth out any excess on the top
Using a double boiler, melt chocolate and slowly add in heavy cream. Stir until fully combined and smooth.
Frost cupcakes and place on a rack, allowing them to dry.
Once dried, create a swirl design on the top of each cupcake. Enjoy!