In a large mixing bowl, add the all-purpose flour, cocoa powder, baking powder, and kosher salt, and set aside. In another bowl, add the sugar, heavy cream, vegetable oil, eggs, and vanilla, and mix until smooth. Pour the wet ingredients into eh dry ingredients and mix well, slowly whisking in the water until the batter is smooth.
Preheat the oven, to 300 degrees F. Fill the muffin tin or cupcake pan with batter, about 2/3 way full. Place the muffin pan into the oven and cook for 18-23 minutes, or until the toothpick inserted into the middle of the cupcakes comes out clean. Let cool before transferring the cupcakes to a wire rack for cooling.
While the cupcakes are cooling, make the filling by adding the butter to a large mixing bowl, beating with a hand mixer, and mixing until smooth. Fold in the marshmallow cream and mix well. Add in the powdered sugar, and mix until smooth. Add about 3 tablespoons of the heavy cream and mix until well combined. Then mix for another 4-5 minutes, until fluffy and smooth. If you want a thinner filling, add a couple of teaspoons of heavy cream.
Add the filling to a piping bag fitted with a piping tip that can pierce your cupcakes. Place the piping tip into the center of the cupcake and fill the inside of the cupcake. Continue to fill the remaining cupcakes.
Add the chopped chocolate to a medium size bowl. Heat the cream just until it starts to simmer, then pour the heated cream over the chocolate, and let sit for about 5 minutes. Whisk to combine, and mix until it's smooth.
Dip the tops of the cupcakes into the glaze, or use a butter knife to add the glaze to the cupcakes,
Take any remaining filling and pipe a curly design on each cupcake.