Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the softened unsalted butter, light brown sugar, and white granulated sugar. Beat until light and fluffy, about 2-3 minutes.
Add the large egg and the cup of Nutella to the mixture. Beat on low speed until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, cornstarch, and salt. Gradually add to the wet ingredients, mixing on low speed until just combined.
Scoop the dough onto a baking sheet lined with parchment paper, leaving about 2 inches between each cookie.
Bake for 10-12 minutes, or until the edges are lightly golden. The centers may look slightly underbaked.
Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
