Pre-heat oven to 350F (180C), place 6 cupcake sleeves in a 6 tin muffin pan.
Make the frosting first, in a large bowl add the mascarpone, Nutella, sugar and cream, beat until very thick. Refrigerate for one hour. (while cupcakes are baking and cooling).
In a large bowl whisk together the sugar, flour, cocoa, baking powder, baking soda and salt, then add the egg, milk, vanilla and oil beat on medium speed for 2 minutes.
Add the boiling water and stir with a wooden spoon or spatula (do not beat) to combine. Pour into prepared cupcake pan and bake for approximately 15 minutes (check with a toothpick for doneness). Let cool completely before frosting. Enjoy!
For room temperature ingredients remove from the fridge 45-60 minutes before using. If your home is cool even a couple hours is fine.