I'm on my third round of this dessert tonight, and it's unbelievably tasty

Pour the batter into the prepared pan and spread it evenly. Bake for 10-12 minutes, or until the cake springs back when lightly touched.
While the cake is baking, lay a clean kitchen towel on a flat surface and dust it with powdered sugar.
Once the cake is done, immediately invert it onto the prepared towel. Carefully peel off the parchment paper.
Starting from a short edge, gently roll the cake and towel together. Let it cool completely on a wire rack.
In a bowl, combine the hot chocolate cocoa mix and heavy cream. Beat until soft peaks form.
Unroll the cooled cake and spread the marshmallow fluff evenly over it, followed by the whipped cocoa cream.
Reroll the cake without the towel, and place it seam side down on a serving platter.
Dust with powdered sugar before serving.