Preheat the oven to 350°F. Line 2 (12-cup) muffin pans with paper cupcake liners.
Gently whisk together the flour, cocoa powder, baking soda, baking powder, and salt in a small bowl. Set aside.
Cream the butter, sugar, and vanilla until fully combined in the bowl of a stand mixer, fitted with a paddle attachment. Add in the eggs and mix until fully incorporated. Scrape down the sides of the bowl.
Add in the dry ingredient mixture, alternating with the sour cream, and mix on low speed until all ingredients are combined. Slowly add the hot coffee and mix on low speed until fully incorporated, scrapping the bowl as necessary.
Scoop the batter into the prepared cupcake pan, filling the liners about 3/4 full. Bake on the bottom rack of the oven for 20–22 minutes, or until a cake tester inserted into the center of the cupcake comes out clean.
Remove the pans from the oven and place on a cooling rack. Let cool for only 10 minutes. Meanwhile, fill a pastry bag, fitted with a large star tip, with the Nutella. Pipe the inside of each cupcake from the top, with enough filling to equal about 1 to 1-1/2 Tbsp.
After the filled cupcakes have cooled completely, pipe a rosette with the remaining Nutella on top and sprinkle with the chopped hazelnuts.
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