In a small bowl, whisk together the flour, hazelnut flour, cocoa powder, espresso powder, baking powder, and salt. Set aside.
In a separate large bowl, whisk together the vegetable oil and granulated sugar until fully combined. Then whisk in the eggs and vanilla until smooth. Whisk in the milk until combined.
Then gently mix in the dry ingredients until fully incorporated. The batter will be thin.
Pour about ¼ cup of batter into each cupcake liner (they should be about halfway full).
Bake at 350°F for 18-22 minutes or until a cake tester comes out clean.
Remove from pan and let cool on wire rack.
Let the chocolate hazelnut cupcakes cool completely before filling and frosting.
Use a cupcake corer to remove the center of each cupcake, then fill with 1-2 teaspoons of Nutella.
Nutella Buttercream
In a large bowl using a handheld or stand mixer fitted with a paddle attachment, cream together the softened butter and Nutella until smooth.
Add in the powdered sugar and salt and mix on low until fully combined.
Then beat on high for 3-5 minutes until the buttercream is super light and airy.
If the frosting in too thick, you can add in 1 tablespoon of cream at a time to thin it out a bit.
Frost the filled chocolate cupcakes and garnish with crushed hazelnuts if desired!
Notes
These cupcakes will last in the fridge for up to 3 days. However, they taste best when served at room temperature! I like to let them sit at room temperature for about an hour before serving.