Start by preheating your oven to 350°F (175°C).
In a large mixing bowl, combine the softened unsalted butter, light brown sugar, and white granulated sugar. Cream together until light and fluffy, about 2-3 minutes.
Add the large egg and Nutella to the creamed mixture. Beat until well combined, scraping down the sides of the bowl as needed.
In another bowl, whisk together the all-purpose flour, cornstarch, and salt. Gradually add this mixture to the wet ingredients, mixing just until combined.
Using a cookie scoop or a tablespoon, portion out the cookie dough onto a baking sheet lined with parchment paper, leaving space between each scoop.
Place the baking sheet in the preheated oven and bake for 10-12 minutes, until the edges are set and the centers are slightly soft.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.