Preheat your oven to 350°F (175°C) for even baking.
In a large mixing bowl, beat the softened unsalted butter, light brown sugar, and white granulated sugar with an electric mixer on medium speed until light and fluffy, about 2-3 minutes.
Add the Nutella and the large egg to the butter-sugar mixture and beat until well combined and smooth.
In another bowl, whisk together the all-purpose flour, cornstarch, and salt to distribute the dry ingredients evenly.
Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined. Avoid overmixing.
Using a cookie scoop or spoon, portion the dough onto a parchment-lined baking sheet, leaving space between each scoop.
Bake for 10-12 minutes until the edges are slightly golden but centers remain soft. They will continue to cook after removal.
Let the cookies cool on the baking sheet for 5 minutes then transfer to a wire rack to cool completely. Enjoy!