In the bowl of an electric mixer cream the butter, brown sugar, granulated sugar, and Nutella for about 2 minutes on medium speed. Scrape down the sides of the bowl as needed.
Add the egg and vanilla extract and mix until fully combined.
Add the flour, baking powder, baking soda, cornstarch, and salt to the bowl. Mix until combined. Scrape down the sides of the bowl as needed. Stir in the chocolate chips.
Cover the bowl with plastic wrap and chill in the refrigerator for 4 hours or until dough is cold and quite firm.
Remove the bowl from the fridge and preheat the oven to 375°F. Line a baking sheet with parhcment paper or a silicone baking mat, set aside.
Using a 2 tablespoon sized cookie scoop, portion out the dough. Carefully flatten each of the dough balls (you don't want them too thin. See blog post photos for reference). I like to make a small indent in half of the dough balls (this is where you'll spoon the nutella).
Using a 1 tsp measuring cup, spoon Nutella in the center of half of the flattened dough balls. Place the remaining half of the flattened dough balls overtop of the nutella filled cookies. Pinch the border of the cookies to keep the nutella from spilling out. Gently roll the dough ball between your hands to carefully close all seams.
Bake 4 cookies per sheet, keeping about 3 inches between each dough ball.
BAke for 10-12 minutes. REmove from the oven and allow the cookies to cool on the pan for 5 minutes then transfer to a wire rack to cool completely.