• Preheat oven to 350°F. Line a muffin pan with paper liners or grease with cooking spray.
• In a small bowl, combine the hot coffee and cocoa powder. Whisk until smooth. Set aside to cool. In a separate bowl, combine the flour, salt and baking soda.
• In the bowl of a stand mixer fitted with a paddle attachment, or in a bowl with a hand-held mixer, beat the sugar and eggs until pale and thick, about 3 minutes. Add the sour cream, and then add the vegetable oil. Add the dry ingredients in 3 additions, alternating with the cocoa mixture. Mix until smooth.
• Fill the muffin cups ⅔ full. Bake for 17-20 minutes, or until the tops of the cupcakes bounce back when touched. Let cool in the pan 5 minutes, then transfer to a rack to cool cool completely.

!To make the frosting:

• Beat the powdered sugar, butter, Nutella and ⅓ cup of the sour cream on medium speed until smooth. Add more sour cream if necessary to achieve a spreadable consistency. Increase speed to high and beat for an additional 1-2 minutes until light and fluffy. Frost cupcakes as desired.
• Store in an airtight container at room temperature for up to 3 days.