In a large bowl, whisk together the flour, cornstarch, baking soda and salt together. Set aside.

Using a hand or stand mixer with the paddle attachment, on medium-high speed beat the butter and ¼ cup of Nutella together until completely smooth. Add in both sugars and mix until fluffy. Beat in the egg, egg yolk, and vanilla until combine. Scrap down the sides as needed. Turning the mixer on low speed, add the dry ingredients in ¼ cup increments. Add the chocolate chips until combined. Beat in the remaining ¼ cup Nutella for 5-10 seconds so it doesn't fully mix.

Cover the dough and chill for 30 minutes. This gives the chance for the butter to firm up slightly.

Preheat the oven to 350F degrees. Line two baking sheets with parchment paper or silicone baking mats (preferred.)

Scoop 1 Tablespoon of dough and roll into taller balls. Bake the cookies for 10 minutes, until slightly golden around the edges. The cookies may look under baked, but that's OK. Allow the cookies to cool for a few minutes on the baking sheet before transferring to a wire rack to cool completely.

Cookies stay fresh in an air tight container for up to a week.

*The first ¼ cup of the Nutella is to be mixed in at the beginning. The second ¼ cup will be mixed in at the end.