First start by preheating the oven to 350F then living your baking sheet with parchment paper or a silicone mat.
In a medium bowl add in the flour, the cocoa powder, the baking powder, and the salt. Whisk to evenly distribute the cocoa powder and the baking powder into the flour then set aside.
In a medium saucepan, melt the butter, once the butter is melted add in the chocolate chips and stir until fully melted. Set aside.
In a stand mixer bowl add in the room temperature egg, the vanilla, the brown sugar, and the granulated sugar and whip until light and fluffy. This will take about 5 minutes. Add the chocolate mixture to the egg mixture and gently fold it in. Once that's incorporated add in the dry ingredients, fold again just until the flour disappears. Add in the chopped toasted hazelnuts and give it one last fold.
Using a small cookie scooper, scoop out 16 equally sized cookie dough balls, making sure to place them at least 1 inch apart from each other since they will spread. Place in the oven and bake for 10 minutes. Let the cookies cook for 5-10 minutes on the baking sheet then enjoy!