Preheat the oven to 350°F.

Line a 12-cup muffin tin with liners.

Whisk the flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl.

Whisk the eggs, sugar, oil, and vanilla in a separate bowl until smooth.

Add the dry ingredients and buttermilk, alternating adding small portions of each at a time, mixing until combined.

Divide the batter evenly into the liners.

Bake for 18–20 minutes, or until the toothpick test comes out clean. You can also gently press the center of the cupcakes with your finger. If they bounce back, they are done. Cool completely.

Beat the butter and confectioner’s sugar in the bowl of a stand mixer with the paddle attachment until fluffy.

Mix in the marshmallow creme, vanilla, and heavy cream until smooth.

Transfer the filling to a piping bag with a small round tip.

Use a small knife or the piping tip to make a hole in the top of each cupcake.

Pipe filling inside, then smooth the top.

Heat the heavy cream until it is steaming.

Place the chopped chocolate and butter in a small heat-safe bowl.

Pour the hot cream over the chopped chocolate and butter. Let it sit for 1–2 minutes untouched, then stir until smooth.

Whisk in the confectioner’s sugar until the mixture thickens slightly. Let cool for 5–10 minutes to reach a dip-able consistency.

Hold each cupcake upside down and dip the top of the cupcake into the chocolate mixture, letting excess drip off. Flip upright and let it set before adding the white swirl.

Mix confectioner’s sugar and milk in a small bowl until it becomes thick but maintains a pipeable consistency.

Transfer to a piping bag with a fine tip and pipe the classic swirl on top.

Let the icing set before serving.