Preheat the oven to 350 F or 180 C. Line 2 cupcake pans with 18 cupcake liners.
In a bowl, combine all the dry ingredients, and whisk until combined.
In another bowl, beat together the butter and sugar until light and fluffy.
Scraping down the sides of the bowl, add in the eggs and vanilla extract, beat until well incorporated.
Alternate with the flour mixture and the buttermilk mixture, until everything is well mixed.
Do not overbeat! Use a spatula to scrape down the sides of the bowl, making sure everything is combined.
Set aside 3/4 cup of the batter.
Fill each muffin liner about half-way full. Top with a teaspoon or small dollop of Nutella.
Spoon the reserved batter on top of the Nutella, making sure the nutty goodness is covered.
Bake for 23 minutes, or until a toothpick inserted comes out clean.
When cooled, frost with Nutella frosting (below), and top off with grated chocolate and hazelnuts.