Preheat the oven to 375 degrees F (190 degrees C) and line a baking sheet with parchment paper or a silicone mat.
In a bowl, whisk together the All-Purpose Flour (1 1/4 cup), Unsweetened Cocoa Powder (3/4 cup), and Baking Soda (3/4 teaspoon) together to fully combine. Set the bowl aside.
In the bowl of a stand mixer, combine the Unsalted Butter (1/2 cup), Salted Butter (4 tablespoon), Granulated Sugar (1 cup), and Dark Brown Sugar (2/3 cup). Cream them together thoroughly with the paddle attachment until it is a light and fluffy mixture.
Then, beat in the Nutella® (1/2 cup). Add in Egg (2) one at a time until they are completely mixed in. Then slowly add in the dry ingredient mixture until just combined.
Turn off the mixer and switch to a rubber spatula to gently fold in the Ferrero Rocher® Chocolate (9).
Use a 1.5 inch cookie scoop to scoop up perfect round portions of the batter. Spread the scoops out evenly onto a baking sheet and press each ball of dough down to flatten it into a nice disk.
Bake the chocolate hazelnut cookies for about 15 minutes or until the edges just start to get crisp and they are cooked through.
Take them out when they're done and let them sit for a few minutes to cool. Transfer to a cooling rack and enjoy!