Preheat your oven to 350°F. Line a cupcake pan with 12 paper lines. Set it aside.
In a large bowl, whisk together the all-purpose flour, hazelnut flour, baking powder, salt, and granulated sugar until combined.
Add in the rest of the cupcake ingredients-- this will be the vegetable oil, eggs, vanilla extract, and whole milk. Whisk until combined and the cupcake batter is formed.
Pour the batter evenly in the liners, making sure to only fill them about ⅔ of the way full.
Bake the cupcakes for 18-22 minutes. The cupcakes should spring back to the touch. Allow the cupcakes to cool in the pan for a few minutes, then transfer them to a cooling rack to finish cooling completely.
Making the Frosting
Cream the unsalted butter and chocolate hazelnut spread for 2 minutes until fluffy and smooth.
Add in the the powdered sugar, cocoa powder, heavy cream, and salt. Whip everything together until combined. Once combined, beat the frosting on a medium speed for about 2 minutes, until the buttercream is light and fluffy.*
Spread or pipe the frosting onto the cooled cupcakes. Enjoy!
Notes
*For stiffer frosting, add another ¼ cup of powdered sugar. For softer frosting, add another tablespoon of heavy cream.