Preheat the oven to 325°F / 165°C and line a 12-count, regular sized muffin tin with cupcake liners.

Now add the dry ingredients into the wet ingredients in 2-3 batches, mixing slowly and increasing the speed until just combined. The batter will be very dark and thick, almost like a thin chocolate ganache.

Spoon or scoop the cupcake batter into the lined muffin tin. Each liner should be a little over halfway full. Continue until all the batter is used, making each one roughly the same amount. Place the muffin pan into the center of the oven and bake for 18-22 minutes. A toothpick inserted into the center of a cupcake should come out mostly clean with a few pieces of cupcake on it. Allow them to cool in the pan for at least 5-10 minutes before removing.

While the cupcakes are baking, start on the filling.

In a microwave safe bowl, add ¾ teaspoon unflavored gelatin and 3 tablespoons of water. Stir to combine and let sit for 5 minutes.

After 5 minutes, give it a quick stir and then microwave 30 seconds on high. If needed, keep microwaving in 10 second intervals until the water is bubbling hot. In a mixing bowl, add 4 tablespoons of unsalted butter, 1 teaspoon vanilla extract, a pinch of salt, and the hot gelatin water. Use a hand mixer or whisk vigorously until the butter has melted and mixed with the gelatin.

Add the 7oz container of marshmallow crème and continue mixing or whisking vigorously until you have a thinner, smoother marshmallow mix. Cover and refrigerate for 20-30 minutes while the muffins finish baking and cooling.

While the marshmallow filling sets up and the cupcakes are cooling, make the hot chocolate buttercream.

In a large mixing bowl, sift 3 ½ cups of powdered sugar and a ½ cup of Dutch-process cocoa powder together with a pinch of salt. This is optional, but I find sifting the powdered sugar for buttercream reduces the chances of any graininess in the final product.

In the bowl of a stand mixer fitted with the paddle attachment, or in a mixing bowl with a hand mixer, add 1 cup of softened butter. Mix on medium speed for a minute or two, then add about a cup or so of the cocoa-sugar mixture. Continue mixing on medium speed for 2-3 minutes until the butter is light and fluffy.

Add 1 teaspoon of vanilla extract and the rest of the cocoa-sugar mixture in 2-3 batches, mixing at a low speed and speeding up as the powdered sugar incorporates. When you add the final amount of powdered sugar, add most of the ¼ cup of heavy cream as well. At this point you can switch the paddle attachment for the whisk attachment, but either one will work.

Mix slowly at first, then continue to increase the speed to high and let it whip together for 2-3 minutes. It should be thick enough to hold its shape, but thin enough to be able to pipe or spread. If it feels too thick, add more heavy cream a teaspoon at a time. If it feels too thin, add more powdered sugar a tablespoon at a time.

Set aside until the cupcakes are fully cooled. If your kitchen tends to run a bit warm, you can refrigerate the buttercream until ready to decorate.

Once cooled completely, it’s time to fill and decorate the cupcakes.

Use a cupcake corer to remove part of the center of the cupcakes. Alternatively, use a sharp paring knife and cut into the cupcake at a 45° angle about a ¼” from the edge. Work your way around the cupcake in a circle and remove the cone shaped piece. In both methods, remove all but a ¼” of the top of the removed piece and set aside.

Scoop or spoon about a tablespoon of the marshmallow filling and place into the hole of the cupcake. Use enough to fill it and then replace the top of the cupcake. Continue for all 12 cupcakes. You should have more than enough filling for all cupcakes.

Now, fill a piping bag with the chocolate buttercream and decorate the tops of the cupcakes. Start on the outer edge of the cupcake and make a loop, slowly heading towards the center of the cupcake. Continue making this loop, going upwards until you’re in the center and finish it off be pressing down slightly, stop piping, and pull straight up.

For reference I used both a Wilton 2D and Wilton 6B piping tip for these. Both made pretty patterns.

Decorate with mini marshmallows or sprinkles and serve.