Before you start, gather all your ingredients and let the butter soften at room temperature.
In a large mixing bowl, combine the softened unsalted butter, light brown sugar, and granulated sugar. Beat until light and fluffy, about 2-3 minutes.
Stir in the heaping 1/3 cup of Nutella until well incorporated. Add in the large egg and vanilla extract, mixing until combined and smooth.
In another bowl, whisk together the all-purpose flour, cornstarch, baking soda, and a pinch of salt. Gradually add this to the wet ingredients, stirring until just combined.
Gently fold in the semi-sweet chocolate chips, ensuring they are evenly distributed throughout the dough.
Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 30 minutes.
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Once the dough is chilled, use a cookie scoop or tablespoon to portion out the dough onto the prepared baking sheet.
Take a 1/4-ounce chunk of dark chocolate and press it gently into the center of each cookie dough ball.
Place the baking sheet in the preheated oven and bake for 10-12 minutes, or until the edges are set but the centers still look soft.
Remove the cookies from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack.
