* Add the butter to a small saucepan and cook over medium heat until melted and browned, stirring occasionally.
* Remove the browned butter from the heat and immediately add the 8 oz semisweet chocolate chips.
* Stir until the chocolate is completely melted and smooth.
* Add the granulated sugar and brown sugar and mix until combined.
* Add the eggs, vanilla extract, and hazelnut extract.
* Mix until the batter is smooth and glossy.
* In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
* Fold the dry ingredients into the chocolate mixture just until no dry streaks remain.
* Cover the cookie dough and refrigerate for **1 hour**.
* While the dough chills, finely chop the hazelnuts.
* Cut each Ferrero Rocher chocolate in half and set aside.
* Preheat the oven to **350°F**.
* Line a baking sheet with parchment paper.
* Scoop the chilled dough using a 2-inch cookie scoop and place the cookies a few inches apart on the prepared baking sheet.
* Bake for **12–15 minutes**, until the edges are set but the centers still look slightly soft and fudgy.
* Allow the cookies to cool on the baking sheet for about 5 minutes.
* Transfer the cookies to a wire rack and cool completely.
* Melt the milk chocolate chips until smooth.
* Stir the chopped hazelnuts into the melted milk chocolate.
* Spoon a small amount of the chocolate-hazelnut mixture onto the center of each cooled cookie.
* Place one Ferrero Rocher half on top of each cookie while the chocolate is still soft.
* Transfer the finished cookies to the refrigerator.
* Chill until the chocolate topping is completely firm.
* Store covered at room temperature or refrigerated until ready to serve.