Preheat oven to 325°F. Spray a 10-inch Bundt pan with nonstick cooking spray.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, cream cheese, and sugar until light and fluffy, about 3 to 5 minutes.

Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl as needed. Mix in the vanilla.

In a separate bowl, whisk together the cake flour, baking powder, cocoa powder, and salt.

With the mixer on low, add about half of the flour mixture to the butter mixture. Mix until combined, then add the remaining flour mixture. Mix just until combined, scraping down the sides of the bowl as needed.

Pour the batter into the prepared Bundt pan and smooth the top.

Bake for 1 hour to 1 hour 15 minutes, beginning to check for doneness at about 55 minutes. The cake is done when a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.

Let the cake cool in the pan for 5 to 10 minutes, then carefully invert it onto a wire rack. Let it cool completely before decorating.

When ready to decorate, add the marshmallow creme, heavy whipping cream, and vanilla to a saucepan over low heat.

Heat, stirring frequently, for 3 to 5 minutes, or until the mixture is smooth and fully combined.

Remove from the heat and let it cool slightly. The sauce should still be pourable but thick enough to slowly drip down the sides of the cake.

Place the cooled cake on a serving platter.

Spoon the mallow sauce over the top of the cake, letting some drip down the sides.

While the sauce is still sticky, arrange the mini marshmallows over the top.

Use a fine-mesh sieve to lightly dust the cake and marshmallows with hot cocoa mix.

Slice and serve. Serve any extra warm mallow sauce on the side, if desired.