Preheat your oven to 350 degrees. Line 2 muffin pans with paper liners.
Combine the ingredients in the bowl of an electric mixer. Stir until smooth and fully combined with the paddle attachment.
Fill cupcake liners ¾ full. Bake for 18 minutes or until a toothpick comes out clean.
For the filling:
Whisk the butter with the marshmallow until fully combined. Add the vanilla and powder sugar and mix until incorporated. Place in a plastic sandwich bag, seal, and snip the edge. Push down into the cooled cupcake and lightly squeeze until full.
For the ganache: Heat the cream just to a boil. Pour over the chocolate chips and allow to sit 3 minutes. Stir until melted. Spoon ganache onto each filled cupcake.