Preheat your oven to 350°F (175°C). Line your cupcake pan with paper liners to make removing the cupcakes a breeze.
In a mixing bowl, combine the 1 cup of cocoa powder with 1 cup of boiling water. Stir until smooth and let it cool slightly. This will enhance the chocolate flavor.
In another bowl, whisk together the 1 ½ cups of all-purpose flour, 1 teaspoon of baking soda, and ½ teaspoon of salt. Set aside.
In a large mixing bowl, beat together 1 cup of unsalted butter, 1 cup of sugar, and ½ cup of brown sugar using an electric mixer until light and fluffy.
Add in the 3 large eggs, one at a time, mixing well after each addition. Then mix in the 2 teaspoons of vanilla extract.
Gradually add the dry flour mixture to the butter mixture, alternating with the 1 cup of buttermilk and the chocolate mixture. Start and end with the flour. Mix until just combined.
Scoop the batter into the prepared cupcake liners, filling each about 2/3 full. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. Remove from the oven and let cool completely.
In a mixing bowl, beat together 6 tablespoons of unsalted butter and 1 cup of confectioners' sugar until fluffy. Add in the 1 cup of marshmallow creme, 1 teaspoon of vanilla extract, and 2 tablespoons of heavy cream. Mix until well combined.
Once the cupcakes are cool, use a small knife or a cupcake corer to remove the center of each cupcake. Fill each hole with the marshmallow filling.
In a clean mixing bowl, beat together 8 oz of cream cheese and 1 cup of unsalted butter until smooth. Add in 2 teaspoons of vanilla extract and ¾ cup of cocoa powder. Gradually add 3 to 4 cups of confectioners' sugar until you reach your desired frosting consistency.
Using a pastry bag or a knife, frost the tops of your filled cupcakes with the chocolate frosting. For an extra touch, sprinkle some gold cupcake gems on top!
