Preheat the oven to 350℉. Prepare muffin tins with 24 cupcake liners or grease with non-stick spray.

In a large bowl, whisk together the melted butter, oil, sugar, vanilla, vinegar, and eggs until well combined. Add the sour cream and milk and whisk until incorporated.

In another bowl, whisk together the flour, sifted cocoa powder, baking powder, baking soda, and salt. Pour the dry ingredient mixture into the bowl with the combined wet ingredients and stir just until no streaks of flour remain. Do not overmix!

Distribute the batter evenly between the 24 cupcake liners in the prepared pans, filling each liner about half full. Bake in the preheated oven for 12-16 minutes or until a toothpick inserted into the center comes out clean. Let cool in the pans for 10 minutes before transferring to a wire rack to cool completely before frosting.

In a small bowl, stir the heated whipping creaming and hot chocolate powder mix until the powder is completely dissolved. Let cool to room temperature.

In a large bowl using an electric handheld mixer, blend the softened butter and cooled hot chocolate/cream mixture on medium speed until smooth. Sift in the powdered sugar and cocoa and mix until combined. Turn up the mixer to high speed. Lastly, add the vanilla extract and 1-2 more tablespoons of cold whipping cream and mix at high speed until a smooth, fluffy consistency is reached.

Pipe onto the fully cooled cupcakes and top with a sprinkle of mini dehydrated marshmallows before the surface of the frosting dries. (The dehydrated marshmallows will get squishy from the humidity so I recommend waiting to add them on top until right before serving.)